A Reversible Molecular Switch Based on the Biphenyl Structure

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 (phi) 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, phi similar to 28 degrees) and an "opened" species (disulfide bridge reduced, phi similar to 65 degrees). 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.