The 3,4-dimethoxybenzyl group as solubilizing protective group for the in situ deprotection/deposition of extended aromatic thiolate monolayers

While self-assembled monolayers (SAMs) of aromatic thiolates are frequently used in a wide range of applications, their formation is often hampered by the low solubilities of their precursors. Here we introduce the 3,4-dimethoxybenzyl group as a protective group for the thiol moiety, which increases the solubility and stability of the precursor, but becomes cleaved off during monolayer formation, especially at elevated temperature (60 °C) and in presence of protons (trifluoroacetic acid). For a series of substituted terphenylthiols as model systems, it could be demonstrated by using ellipsometry, infrared-reflection absorption spectroscopy, and scanning-tunneling microscopy that the resulting SAMs have the same structure and quality as the ones obtained from the respective unprotected thiols. The protective group has the additional advantage to be stable under Pd-catalyzed C–C bond formation reaction conditions, facilitating the syntheses of the respective precursors.