Hydrogen Bonding in Thioether Self-Assembly
McGuire, Allister F.
- Thioethers represent an interesting alternative to thiols as monomers for molecular self-assembly on metal surfaces. In contrast to thiols, and due to their unique adsorption geometry, thioethers offer the opportunity to control molecular packing in the dimension parallel to the surface, and their weaker surface binding can lead to monolayers with a lower defect density. In a step towards designing ... read morethioether monolayers with multiple functionalities, we have investigated the molecular-scale assembly of 3-(methylthio)propanol on Au(111). Scanning tunneling microscopy reveals that the hydroxyl groups drive the formation of an array of novel structures that are not observed with the analogous thioether, butyl methyl sulfide. The hydrogen-bonding-driven ordering yields linear chains and hexamer rings that are very similar in structure to methanol assemblies on Au(111). At near-monolayer coverage, very ordered monolayers are observed. The adsorption is strong enough to lift the native herringbone reconstruction of the Au(111) surface but stops short of removing additional atoms, as is the case with thiols. While these monolayer structures are similar to those of non-functionalized butyl methyl sulfide, hydrogen bonding between adjacent rows leads to lamellar structures with a hydrophilic core and hydrophobic exterior. As such, these assemblies are one-dimensional analogues of the lipid bilayer.read less