Gold–Carbon Contacts from Oxidative Addition of Aryl Iodides

Abstract

Aryl halides are ubiquitous functional groups in organic chemistry, yet despite their obvious appeal as surface-binding linkers and as precursors for controlled graphene nanoribbon synthesis, they have seldom been used as such in molecular electronics. The confusion regarding the bonding of aryl iodides to Au electrodes is a case in point, with ambiguous reports of both dative Au−I and covalent Au−C contacts. Here we form single-molecule junctions with a series of oligophenylene molecular wires terminated asymmetrically with iodine and thiomethyl to show that the dative Au−I contact has a lower conductance than the covalent Au−C interaction, which we propose occurs via an in situ oxidative addition reaction at the Au surface. Furthermore, we confirm the formation of the Au−C bond by measuring an analogous series of molecules prepared ex situ with the complex Au I (PPh 3 ) in place of the iodide. Density functional theorybased transport calculations support our experimental observations that Au−C linkages have higher conductance than Au−I linkages. Finally, we demonstrate selective promotion of the Au−C bond formation by controlling the bias applied across the junction. In addition to establishing the different binding modes of aryl iodides, our results chart a path to actively controlling oxidative addition on an Au surface using an applied bias.

Single‐Molecule Electrochemical Transistors

“…This method provides a straightforward way to achieve the same effect as electrochemical gate expect for the reaction occurs on the tip, which has been demonstrated experimentally through cyclic voltammetry (CV) measurements and has been widely used for constructing the specific single-molecule junctions through facile electrochemical reaction on the anchoring groups in their subsequent studies. [43][44][45][46] However, bias voltage for the electrochemical reaction is about five times larger than that of the conventional three-electrode electrochemical system, suggesting that a 20% gating efficiency (β = 0.2) is for the STMbased SMECTs with two-electrode configuration (Figure 2e). [37] Moreover, the field-induced breakdown of single-molecule junctions is more possible to occur at large bias voltage, [41,47] and the tunable range for the molecular resonance energy is therefore limited.…”

Spectroscopic Evidence for a Covalent Sigma Au–C Bond on Au Surfaces Using 13C Isotope Labeling

“…In addition, Au−C bonded single-molecule junctions exhibit a much larger conductance than most other linkages. 14,21 In spite of the intense research interest in the Au−C bonding on Au surfaces, direct experimental evidence of its existence is still missing to support the calculations of its nature. 22,23 X-ray photoelectron spectroscopy (XPS) is typically applied to investigate interactions for modified metal surfaces, including Au.…”

“…The considerable interest in Au–C bonding is due in part to its significant robustness and excellent ambient, thermal, and chemical stability. ,, In fact, by mechanically breaking the junction, it was shown that the Au–C bonding results in a more robust junction than the corresponding Au–N bonding obtained if the same molecule was connected using amine linkers. In addition, Au–C bonded single-molecule junctions exhibit a much larger conductance than most other linkages. , …”

Single-Molecule Junctions with Highly Improved Stability

“…scanning-tunneling microscopy break junction (STM-bj). [26][27][28][29][30][31] or mechanically controlled breakjunction (MCBJ), [32][33][34][35][36] and graphene-based SMJs have also recently appeared in the litterature. [37][38][39] In most STM-bj experiments, the conductance is continuously recorded as an atomic contact is broken in a solution of molecules, and a conductance plateau, indicating the formation of a SMJ, is observed when a molecule comes between the two electrodes during the pulling process.…”