In contrast to silicon-based transistors, single-molecule
junctions
can be gated by simple mechanical means. Specifically, charge can
be transferred between the junction’s electrodes and its molecular
bridge when the interelectrode distance is modified, leading to variations
in the electronic transport properties of the junction. While this
effect has been studied extensively, the influence of the molecular
orientation on mechanical gating has not been addressed, despite its
potential influence on the gating effectiveness. Here, we show that
the same molecular junction can experience either clear mechanical
gating or none, depending on the molecular orientation in the junctions.
The effect is found in silver–ferrocene–silver break
junctions and analyzed in view of ab initio and transport calculations,
where the influence of the molecular orbital geometry on charge transfer
to or from the molecule is revealed. The molecular orientation is
thus a new degree of freedom that can be used to optimize mechanically
gated molecular junctions.