The interaction of 4-[4'-(phenylethynyl)-phenylethynyl]-benzenethiols (PPBSH) with Au(1 11) 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. (C) 2003 Elsevier Science B.V. All rights reserved.