Rotation-libration in a hierarchic supramolecular rotor-stator system: Arrhenius activation and retardation by local interaction

Fourfold symmetric zinc-octaethylporphyrin (OEP) has been incorporated in the holes of the hexagonal molecular network generated by thermal dehydrogenation of 4,9-diaminoperylenequinone3,10- diimine (DPDI) on a Cu(111) surface and displayed hindered rotation; the reorganization between the potential minima, a rotation-libration, which is characterized by an activation energy of E-D=0.17 +/- 0.03 eV, has been monitored in the STM tunnelling currents as a bi-state ''switching''.