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.

Direct conversion of solar energy to mechanical work promises higher efficiency than multistep processes, adding a key tool to the arsenal of energy solutions necessary for our global future. The ideal photomechanical material would convert sunlight into mechanical motion rapidly, without attrition, and proportionally to the stimulus. We describe crystals of a tetrahedral isocyanoazobenzene−copper complex that roll continuously when irradiated with broad spectrum white light, including sunlight. The rolling results from bending and straightening of the crystal due to blue light-driven isomerization of a highly twisted azobenzene ligand. These findings introduce geometrically constrained crystal packing as a strategy for manipulating the electronic properties of chromophores. Furthermore, the continuous, solar-driven motion of the crystals demonstrates direct conversion of solar energy to continuous physical motion using easily accessed molecular systems.

Recent interest in potassium-doped p-terphenyl has been fueled by reports of superconductivity at T c values surprisingly high for organic compounds. Despite these interesting properties, studies of the structure−function relationships within these materials have been scarce. Here, we isolate a phase-pure crystal of potassium-doped p-terphenyl:Emerging antiferromagnetism in the anisotropic structure is studied in depth by magnetometry and electron spin resonance. Combining these experimental results with density functional theory calculations, we describe the antiferromagnetic coupling in this system that occurs in all 3 crystallographic directions. The strongest coupling was found along the ends of the terphenyls, where the additional electron on neighboring p-terphenyls antiferromagnetically couple. This delocalized bonding interaction is reminiscent of the doubly degenerate resonance structure depiction of polyacetylene. These findings hint toward magnetic fluctuation-induced superconductivity in potassium-doped p-terphenyl, which has a close analogy with high T c cuprate superconductors. The new approach described here is very versatile as shown by the preparation of two additional salts through systematic changing of the building blocks.

A single‐molecule method has been developed based on the scanning tunneling microscope (STM) to selectively couple a series of aniline derivatives and create azobenzenes. The Au‐catalyzed oxidative coupling is driven by the local electrochemical potential at the nanostructured Au STM tip. The products are detected in situ by measuring the conductance and molecular junction elongation and compared with analogous measurements of the expected azobenzene derivatives prepared ex situ. This single‐molecule approach is robust, and it can quickly and reproducibly create reactions for a variety of anilines. We further demonstrate the selective synthesis of geometric isomers and the assembly of complex molecular architectures by sequential coupling of complementary anilines, demonstrating unprecedented control over bond formation at the nanoscale.

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