  Reversible opto-mechanical molecular switch based on a single azobenzene
molecule suspended via thiolate links between realistic models of gold tips is
investigated. Using a combination of the transfer matrix technique and density
functional theory we focus on conductance of the nano-device in the two
(meta)stable cis and trans junction conformations. We find the conductance of
both conformations to be broadly similar. In qualitative agreement with related
experiments, we find that the same nano-device with one/two methylene linker
group(s) inserted on one/both ends of the azobenzene molecule is driven into
tunneling regime and reduces the conductances by up to two orders of magnitude,
again almost uniformly for both conformations. These results clarify the huge
differences in switching ratios found previously and indicate that this
nano-device is not particularly suited for use as a molecular switch based on
conductance change.
