  We demonstrate that nanocavity plasmons generated a few nanometers away from
a molecule can induce molecular motion. For this, we study the well-known rapid
shuttling motion of zinc phthalocyanine molecules adsorbed on ultrathin NaCl
films by combining scanning tunneling microscopy (STM) and spectroscopy (STS)
with STM-induced light emission. Comparing spatially resolved single-molecule
luminescence spectra from molecules anchored to a step edge with isolated
molecules adsorbed on the free surface, we found that the azimuthal modulation
of the Lamb shift is diminished in case of the latter. This is evidence that
the rapid shuttling motion is remotely induced by plasmon-exciton coupling.
Plasmon-induced molecular motion may open an interesting playground to bridge
the nanoscopic and mesoscopic worlds by combining molecular machines with
nanoplasmonics to control directed motion of single molecules without the need
for local probes.
