Synthesis and characterization of self-assembled monolayers of alkylated 1-thiahexa(ethylene oxide) compounds on gold

Self-assembled monolayers (SAMs) of a series of novel linear thiols containing a 1-thiahexa(ethylene oxide) (THEO) moiety, i.e., HS(CH2CH2O)(6)R, where R = C10H21, C10D21, C18H37, and C18D37, were prepared on polycrystalline gold (Au) and characterized by reflection absorption infrared spectroscopy (RAIRS), spectroscopic ellipsometry, surface plasmon resonance (SPR), and contact angle measurements. The SAMs are hydrophobic with contact angles, theta(a) (H2O), of 108 degrees-109 degrees for all surfaces. For all compounds, our data provide evidence for well-ordered monolayers in which the THEO moiety is arranged in a 7/2 helix oriented normal to the substrate. The alkyl group conformation and tilt are similar to the corresponding n-alkanethiol SAMs.