Self-Assembly and Orbital Imaging of Metal Phthalocyanines on a Graphene Model Surface

Metal phthalocyanines (MPc) form a tunable class of molecules, where both the central metal ion and the organic macrocycle can be modified. This allows the electronic properties and self-assembly of these molecules to be tuned over a broad range. We focus on cobalt phthalocyanine (CoPc), copper phthalocyanine (CuPc), and fully fluorinated cobalt phthalocyanine (F16CoPc) and study their self-assembly on epitaxial graphene. We investigate the energetic positions and symmetries of the frontier molecular orbitals by low-temperature scanning tunneling microscopy (STM) and spectroscopy (STS) experiments and density functional theory (DFT) calculations. Our results shed light on the molecular ordering and the energies of molecular orbitals with respect to the graphene Dirac point for the different MPcs. This information will be crucial for using molecular overlayers to modify the electronic properties of graphene.