Aggregation of C₇₀-Fragment Buckybowls on Surfaces: π-H and π-π Bonding in Bowl Up-Side-Down Ensembles

The self-assembly of the C₃₈H₁₄-buckybowl, a fragment bowl of the C₇₀ fullerene, has been studied with scanning tunneling microscopy on the Cu(111) surface. Isolated molecules adsorb bowl opening-up with the center C6 ring parallel to the surface. In extended 2D islands, however, 1/3 of the molecules are oriented such that the bowl opening points down. From a detailed analysis of relative orientation of the molecules, the nature of intermolecular lateral interactions is identified. In densely packed islands, π-π bonding between convex sides of the bowls dominate, while π-H bonding between rim and convex sides plays the important role in small molecular 2D clusters.