A Reversible Molecular Switch Based on the Biphenyl Structure

Abstract

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.

Mechanical Effects on the Electronic Properties of a Biphenyl-Based Molecular Switch

“…39 There, it was shown that this metal/molecule hybrid nanojunction can be stretched by ∼ 8.5Å, before it finally breaks. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 reported in Ref.…”

“…1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 reported in Ref. 39 on the thermodynamics of the reduction reduction and the transport properties of the species involved were based on the first minimum encountered along the stretching pathway.…”

“…The mechanical properties of Au-S-Ox "cis" and "trans" were studied by means of a series of constrained geometry optimizations and the results have already been reported in Ref. 39. For both, Au-S-Ox "cis" and "trans", the energy profile along the stretching pathway displays a sawtooth-like behavior with three well defined minima before the final breakage.…”

“…1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 leads. In our previous work, 39 we had identified the relevance of a Au-C bonding interaction between the Au atoms in the apex of each cluster with a carbon atom in each aromatic ring. This interaction resulted of relevance only for the thiolated bounded species.…”

“…38 In a recent computational study, we have proved the potential of a biphenyl system with a disulfide functionality bridging the aromatic rings as a (electro)chemically triggered molecular switch. 39 The electron transport properties of this molecular system attached on either extreme to gold clusters, which mimicked the tips of two electrodes, by means of a S-Au bond were evaluated. It was shown that the torsion angle, and in turn the transport properties of the molecular junction, can be controlled by means of reducing/oxidizing the disulfide functionality, allowing the system to switch between a "closed" (high conductance) and an "opened" (low conductance) species.…”