Branched Substituents Generate Improved Supramolecular Ordering in Physisorbed Molecular Assemblies

We present an experimental study supported by molecular simulations of the influence of the shape of alkyl side groups on the interactions and self-organization of supramolecular assemblies, built from bis-urea-substituted toluene molecules deposited on Au(111) surfaces. In particular, we demonstrate the crucial importance of the presence of branched alkyl groups (i.e., ethylhexyl) that allow two adjacent supramolecular polymers to arrange closer to each other, leading to the formation of molecular “zippers”. Thus, steric constraints at the level of individual molecules can generate improved ordering between neighboring supramolecular polymers interacting with a planar substrate.