Two-dimensional self-assembly of supramolecular structures

We briefly review recent low temperature scanning tunneling microscopy (STM) investigations performed in our laboratory(1-5) on the self-assembly of the dipolar organic molecule 1-nitronaphthalene (NN) adsorbed on the reconstructed Au(lll) surface. NN becomes chiral upon planar adsorption on the gold surface. We observe several coverage-driven structural transformations which are associated with simultaneous changes in the enantiomeric composition of the self-assembled molecular structures. At low coverages almost exclusively decamers with an 8:2 ratio of the enantiomers are formed. In a medium coverage range enantiopure one-dimensional molecular double chains prevail on the surface. Subsequently, molecules with opposite handedness are admired until at monolayer coverage racemic one- and two-dimensional structures coexist. Modeling shows that hydrogen bonding causes the observed self-assembly. A subtle interplay between the electrostatic interactions among the molecules and their interaction with the reconstructed metal surface is the origin of the observed coverage-driven chiral phase transition in two dimensions.