Long-Range Surface-Assisted Molecule-Molecule Hybridization

Metalated phthalocyanines are robust and versatile molecular complexes, whose properties can be tuned by changing its functional groups and central metal atom. Here, we studied the electronic structure of magnesium phthalocyanine (MgPc) - similar in structure and electronic properties to chlorophyll - on Ag(100) via low-temperature scanning probe microscopy (STM/STS/ncAFM) and density functional theory (DFT). Our ncAFM and STS data show that a single isolated MgPc molecule exhibits a flat four-fold symmetric morphology with doubly degenerate, partially populated lowest unoccupied molecular orbitals (LUMOs). Conversely, molecules with adjacent MgPc’s in proximity (within a distance of ~3 nm) show a lift of LUMO degeneracy and symmetry reduction, from four- to two-fold. We explain this interaction by a two-step hybridization process: MgPc orbitals first hybridize with Ag(100), forming molecule-surface orbitals with enhanced spatial extension that then hybridize in turn with neighboring molecules. This work highlights how orbital degeneracies and symmetries of molecular adsorbates can be significantly altered via surface-mediated intermolecular hybridization, over extended distances, having important implications for prospective molecule-based solid-state electronics.