Self-Assembled Monolayers of an Aryl Thiol:  Formation, Stability, and Exchange of Adsorbed 2-Naphthalenethiol and Bis(2-naphthyl) Disulfide on Au

Abstract

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(2-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.

Electron transfer studies on cholesterol LB films assembled on thiophenol and 2-naphthalenethiol self-assembled monolayers

“…This behavior is also typical of aromatic monolayer covered surfaces with poor blocking character towards the redox species [20]. It is generally known that aromatic thiols, due to their highly delocalized π electrons in the aromatic ring and extended conjugation of the molecules do not completely block the electron transfer reactions [22][23][24][25][26][27][28]. This property of the aromatic SAM is made use of in sensor and catalysis studies [25][26][27].…”

Structural and Protecting Properties of Functional Organic Coatings on Copper

“…The exposure of FBT and MBT SAMs to DT could result in adsorption of DT at irregularities (defects/pinholes) present within the thioaromatic SAM (7,17,43,44) and/or in a very slow (measured in days) displacement of the aromatic thiols by DT (17,18). The exchange involves proton transfer at the Cu surface followed by desorption according to the bimolecular mechanism proposed by Scheme 1 (18,38). At the beginning of exchange, filling of pinholes or defects occurs, while at later stages the displacement is more likely to occur (17).…”

“…A structural organization, packing and order of SAM of aromatic thiols can be improved remarkably by the exchange of aromatic thiols with n-alkanethiols (7,15,17,18). If thioaromatic SAMs have a substantial number of defects (pinholes), an exposure to nalkanethiols should result in their preferential adsorption at defect sites (7,17).…”

“…At longer immersion times, a very slow displacement occurs, depending on the stability of aromatic thiol SAMs. The extent of SAM order and stability appears as a key factor in limiting the access of incoming displacer molecules (18).…”

Electrochemical characterization of self-assembled monolayers (SAMs) of thiophenol and aminothiophenols on polycrystalline Au: Effects of potential cycling and mixed SAM formation

“…We have chosen these thiols because they have the comparable chain lengths to that of the aromatic thiols studied in this work. It is also known that the adsorption energy of aliphatic thiols on gold surface is lower in comparison to the energy required to replace an existing aromatic thiol [34][35][36][37][38][39][40][41]. Therefore, it is expected that the added aliphatic thiol and dithiol molecules essentially fill up the pinholes, defects and domain boundaries present within the monolayer resulting in the formation of a compact monolayer.…”