Recent progress in addressing electrically driven single‐molecule behaviors has opened up a path toward the controllable fabrication of molecular devices. Herein, the selective fabrication of single‐molecule junctions is achieved by employing the external electric field. For molecular junctions with methylthio (–SMe), thioacetate (–SAc), amine (–NH2), and pyridyl (–PY), the evolution of their formation probabilities along with the electric field is extracted from the plateau analysis of individual single‐molecule break junction traces. With the increase of the electric field, the SMe‐anchored molecules show a different trend in the formation probability compared to the other molecular junctions, which is consistent with the density functional theory calculations. Furthermore, switching from an SMe‐anchored junction to an SAc‐anchored junction is realized by altering the electric field in a mixed solution. The results in this work provide a new approach to the controllable fabrication and modulation of single‐molecule junctions and other bottom‐up nanodevices at molecular scales.
the reaction dynamics of confined reaction in millimolar concentration scale efficiently. However, NMR, isothermal titration calorimetry, and thermogravimetry are challenging to obtain the dynamic changes during confined reaction at micromolar concentrations (5 × 10 −6 m) relative to conventional reactions, which is due to its complex multimolecular interactions, [10] and the poor solubility results in concentrations in the solution below the detection range of conventional methods. [11] The test methods that can detect the reactants in micromolar concentration include fluorescence spectra and SERS, but fluorescence spectra need to be labeled with fluorescent groups, [12] and SERS requires substrates. [13] Therefore, the application of the above methods in micromolar concentration chemical reaction tracking is still lacking in universality. The single-molecule conductance measurement technique is based on the repeated opening and closing of metal electrodes to form a large number of single-molecule junctions. The electrode forms a nanometer gap during the stretching process, thus achieving the capture of single molecules. [14][15][16] Break junction techniques offer the opportunity to detect the single-molecule electrical signals of the reactants at the singlemolecule scale. [17][18][19][20][21][22][23] Although mass spectrometry can be used to study reactions at low concentrations, this technique cannot reach single-molecule level. Moreover, the high energy of mass spectrometry will affect the weak interaction and reaction. While, this observation based on scanning tunneling microscope-break junction (STM-BJ) technique is lossless and low consumption. Therefore we choose STM-BJ technique to track the confined reaction based on host-guest interaction.The single-molecule conductance measurement of reaction can provide direct evidence for reaction kinetics [24,25] and reaction mechanisms from the molecular level. Recent advances suggested that the single-molecule techniques can track reactions such as Diels-Alder reaction, [26,27] ring cleavage and ring closure reaction, [28,29] cleavage of alkoxyamines, [30] isomerization reactions of cumulenes, [31] aniline coupling, [32] photoswitches of photochromic molecules, [33] and supramolecular interactions are also detected in molecular junctions includeThe host-guest interaction acts as an essential part of supramolecular chemistry, which can be applied in confined reaction. However, it is challenging to obtain the dynamic process during confined reactions below micromolar concentrations. In this work, a new method is provided to characterize the dimerization process of the guest 1,2-bis(4-pyridinyl) ethylene in host cucurbit[8]curil using scanning tunneling microscope-break junction (STM-BJ) technique. The guest reaction kinetics is quantitatively by nuclear magnetic resonance (NMR) and in situ single-molecule junctions. It is found that in the single-molecule conductance measurements, the electrical signals of the reactants with a concentration as low as 5 × 10 −6 m a...
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