Controlling the Ligand Spin of Surface-Adsorbed Double-Decker Phthalocyaninato Complexes: A suggestion from theoretical calculations

Single-molecule magnetic materials, which have potential applications in molecular memory and quantum bits, have been synthesized using ligands that possess electronic spins. Unpaired electrons on ligands are strongly affected by substrate adsorption and transfer to the substrate; however, the mechanism behind this phenomenon remains unclear. In this study, we aimed to control the magnetic properties of doubledecker phthalocyaninato (MPc2) complexes as representative single-molecule magnetic materials, and to theoretically investigate the effects of adsorption on unpaired electrons using density functional theory. When MPc2 is absorbed onto metal surfaces, spin elimination caused by electron transfer between the molecule and surface is observed. We showed that the spin elimination by the substrate can be suppressed by delocalization of π-radicals within the ligands; large surface coverage of the substrate; and insertion of a screen layer, such as graphene, between the molecule and the substrate. The key factor of these approaches is to decrease the orbital correlation between the molecule and the substrate in the axial direction perpendicular to the surface.