Inspecting Metal-Coordination-Induced Perturbation of Molecular Ligand Orbitals at a Submolecular Resolution

Molecular states of terpyridine ligands in supramolecular coordination assemblies were investigated by means of scanning tunneling microscopy/spectroscopy conducted at cryogenic temperature. Submolecular-resolved signals manifest that within the molecules, the empty states at the moieties that are directly involved in the coordination are downshifted, whereas the other moieties are unaffected. Theoretical calculations attribute this localized perturbation to the specific characteristics of the ligand’s orbitals; the ligand moieties possess highly localized empty states. Our results demonstrate that it is feasible to electronically modify individual moieties of ligands in supramolecular assemblies by metal coordination.