Cooperative Rotation and Spin State Switching of Molecules in Artificial Arrays

Artificial arrays of tin phthalocyanine molecules have been studied on Pb(100) using scanning tunneling microscopy (STM). The molecules adopt two azimuthal orientations with distinct spin states, which results in a checkerboard pattern in STM images. Upon converting the central molecule by current injection from its pristine state with the Sn ion above the molecular plane to a conformation with Sn between the macrocycle and the substrate, the orientations of all molecules are swapped. This cooperative rotation is modeled by combining the potential energies of the intermolecular and the molecule-substrate interactions.