Interaction of a conjugated phenylene ethynylene trimer with a Au(1 1 1) surface

The interaction of 4-[4′-(phenylethynyl)-phenylethynyl]-benzenethiols (PPBSH) with Au(1 1 1) surfaces has been studied using density functional theory and a cluster model. For PPBSH perpendicular to the surface, the threefold hollow is the most favorable site, but the energy difference between this and the least favorable site is only about 9 kcal/mol. The most stable form of PPBSH on the surface is bent, therefore, PPBSH should only be perpendicular to the surface at higher coverages.