  Impressive advances in nanoscience permit nowadays to manipulate single
molecules and broadly control many of their properties. Still, tuning the
molecular charge and vibrational properties of single molecules embedded in
nanojunctions in broad ranges escaped so far to an efficient control. By
combining theoretical results with recent experimental data, we show that,
under electrochemical control, it is possible to continuously drive a redox
molecule (viologen) between almost perfect oxidized and reduced states. This
yields an unprecedentedly efficient control on both vibrational frequencies and
the surface-enhanced Raman scattering (SERS) intensities. The broad tuning
achieved under electrochemical control by varying the overpotential ("gate
potential") within experimentally accessible ranges contrasts to the case of
two-terminal setups that require high biases, which real nanojunctions cannot
withstand. The present study aim at stimulating concurrent transport and SERS
measurements in electrochemical setup. This may open a new avenue of research
that is not accessible via two-terminal approaches for better understanding the
transport at nanoscale.
