DFT calculations were performed on a biphenyl-based molecule bonded to gold nanoleads in order to evaluate its potential as a reversible molecular switch. The torsion angle (φ) between the aromatic rings may be controlled by means of reducing a disulfide functionality that bridges the two rings, giving rise to a "closed" species (disulfide bridge oxidized, φ ∼ 28°) and an "opened" species (disulfide bridge reduced, φ ∼ 65°). The mechanical properties of the nanojunction formed by this molecular species sandwiched between gold cluster pyramids mimicking metallic electrodes were determined. The thermodynamics of the reduction reaction was studied on the disulfide bridge as well as on the potentially competing anchoring sulfur atoms. A highly favorable product ratio toward the disulfide bridge reduction was found. Conductance values were calculated by means of non-equilibrium Green functions techniques. Interestingly, a significant difference between the closed (high conductance) and opened (low conductance) species was found.

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Using a combination of density functional theory and non-equilibrium Green function calculations, the effect of mechanically stretching a biphenyl-based molecular switch bonded to Au electrodes is studied. Thermodynamic and transport properties of the high and low conducting species are analyzed. A disulfide functionality bridging the aromatic rings is used to switch between the high and low conducting species. The potential of such a system as a molecular device has already been proved [J. Phys. Chem. C 2013, 117, 25724]. Mechanically stretching the molecular junction has major effects on both the thermodynamics of the switching reaction and the conductance ratio between the high and low conducting species involved in the molecular switch. It is also shown that the conductance of each individual species can be modulated by means of an external mechanical force, thus providing a dual switching mechanism for the proposed system.