Supramolecular Organization of Model Polycyclic Aromatic Molecules: Comparison of 2D and 3D Assemblies

The spatial organization of polycyclic aromatic molecules during adhesion on a solid/liquid interface is the key event of a plethora of natural and industrial processes. Herein, we report the supramolecular assembly of violanthrone-79—a model of asphaltenes, an intractable mixture of polycyclic aromatics from crude oil—at the solid-liquid interface between highly oriented pyrolytic graphite (HOPG) and a hydrophobic medium (1-phenyloctane). High-resolution scanning tunneling microscopy revealed that molecules of violanthrone-79 readily self-assemble on the surface in supramolecular “nanoring” structures. The lattice parameters of the 2D unit cell are on the same order as those determined from a bulk single crystal. Transmission electron microscopy showed long-range ordered patterns, and the spacing between the fringes is in agreement with the inter-planar distances between aromatic cores of molecules that are helically arranged around the [001] axis in the 3D crystal. The results confirm that upon adsorption on solid/liquid interfaces, polycyclic aromatic molecules such as violanthrone-79 form supramolecular assemblies by interaction with the substrate and self-association, and this process could be the initial step of deposition of asphaltenes on carbonaceous oil reservoir walls and production tubing.