Investigation of the non-covalent interactions of molecular self-assembly by scanning tunneling microscopy using the association of aromatic structures in pyrene-4,5,9,10-tetraone and phenanthrene-9,10-dione molecules

The self-assembled molecular monolayers of aromatic molecules (pyrene-4,5,9,10-tetraone (PT) and phenanthrene-9,10-dione (PD)) were investigated at the liquid/solid (1-phenyloctane/graphite) interface using scanning tunneling microscopy (STM). High resolution STM images revealed that PT tended to build a chevron pattern with individual peanut-shaped molecule; moreover, PD was apt to form a simple linear chain with single pearl-like molecule. Density functional theory (DFT) calculations employing the state-of-the art method of PBE + vdW^surf revealed that the hydrogen bonding from molecule-molecule interactions (PT-PT, PD-PD) and van der Waals (vdW) forces from building molecule-substrate (PT-graphite, PD-graphite) interactions played noticeable roles in the construction of these supramolecular architectures. By comparing the chemical structural differences between these two types of molecular building blocks, this study concisely and explicitly demonstrates that the advantages, such as structural symmetry and functional groups, possessed by building molecules promote the efficient synergy of multiple intermolecular non-covalent interactions and the feasible self-assembly of different supramolecular monolayers on diverse surfaces.