Tracking Confined Reaction Based on Host–Guest Interaction Using Single‐Molecule Conductance Measurement

Abstract

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...

Emerging sensing platforms based on Cucurbit[n]uril functionalized gold nanoparticles and electrodes

“…Recently, Hong's group reported a novel method to characterize the dimerization process of the guest 1,2-bis(4-pyridinyl) ethylene (BPE) in CB [8] using the STMBJ. 89 By mixing BPE and CB [8], two BPE molecules are encapsulated into the cavity of CB [8], leading to the formation of a BPE dimer (BPE 2 ) upon laser irradiation. Electrical conductance of the BPE monomer, a mixture of 2BPE@CB [8] and BPE, dimerization compound BPE 2 @CB [8] is measured using RT by anchoring the pyridine group.…”

Characterization and Application of Supramolecular Junctions

“… (a) Schematic illustration of the host‐guest system assisted reaction [79] . 2D conductance histograms of the molecule BPE (b), 2BPE@CB[8] complex (c) and the producted BPE 2 @CB[8] (d).…”

“…Reproduced from Ref. [79] with permission. Copyright 2022, Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.…”

“…In 2022, Yuan et al investigated the intermolecular photochemical dimerization reaction of the 1, 2-bis (4-pyridinyl) ethylene (BPE) in the confined chamber of cucurbit [8]uril. [79] Two BPE guests are first preassembled in the cucurbit [8]uril host to form the energetically favorable cis-dimer complex configuration (Figure 18a) that the only parts of each guest body are embedded in the host cavity and the parts out of the host align in the same directions. In this configuration, the conductance of the complex cannot be detected due to the anchoring groups aligned only on one side.…”

The pivotal role of non-covalent interactions in single-molecule charge transport

“…[127][128][129][130] By this means, Yuan et al showed that single-molecule junctions formed in an STM-BJ setup could provide a testbed to detect temporal signals from reactants in ultra-low concentrations, which are invisible to methods such as mass spectroscopy. 131 They used hostguest assembly to study the conductance change during complexation of 1,2-bis(4-pyridinyl)ethylene (BPE) monomer and CB [8], and finally the dimerization product to BPE2@CB [8] upon UV irradiation. As seen in Fig.…”