  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 molecule 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 molecule 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 molecular orbitals geometry on charge transfer to or from the
molecule is revealed. The molecule orientation is thus a new degree of freedom
that can be used to optimize mechanically-gated molecular junctions.
