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Understanding chemical processes at the single-molecule scale represents the ultimate limit of analytical chemistry. Single-molecule detection techniques allow one to reveal the detailed dynamics and kinetics of a chemical reaction with unprecedented accuracy. It has also enabled the discoveries of new reaction pathways or intermediates/transition states that are inaccessible in conventional ensemble experiments, which is critical to elucidating their intrinsic mechanisms. Thanks to the rapid development of single-molecule junction (SMJ) techniques, detecting chemical reactions via monitoring the electrical current through single molecules has received an increasing amount of attention and has witnessed tremendous advances in recent years. Research efforts in this direction have opened a new route for probing chemical and physical processes with single-molecule precision. This review presents detailed advancements in probing single-molecule chemical reactions using SMJ techniques. We specifically highlight recent progress in investigating electric-field-driven reactions, reaction dynamics and kinetics, host–guest interactions, and redox reactions of different molecular systems. Finally, we discuss the potential of single-molecule detection using SMJs across various future applications.
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This content will become publicly available on December 12, 2026
Electrical Catalysis of Forbidden Transitions in Single‐Molecule Devices
Molecular orbital symmetry plays a pivotal role in determining chemical reaction mechanisms. The process of changing chemical reactants into products must transition along a pathway that conserves molecular orbital symmetry to ensure continuity. This principle is so fundamental that reactions that do not conserve symmetry are typically considered “forbidden” due to the high resultant energy barriers. Here, it is demonstrated that it is possible to electrically catalyze these forbidden transitions when a single molecule is bound between two electrodes in a nanoscale junction. A cycloaddition reaction is induced in a norbornadiene (NBD) derivative, converting it to quadricyclane (QC) by utilizing nanoconfinement to place the molecule into a configuration that is far from equilibrium and applying a small voltage to the molecular junction. Traditionally, this reaction can only be induced photochemically due to orbital symmetry selection rules. By directly tracking the reaction dynamics in situ using single‐molecule Raman spectroscopy, it is shown that for this reaction to be electrically catalyzed the molecule must be sterically maneuvered into a configuration near the transition state at the peak of the energy barrier prior to applying the voltage needed to successfully induce the forbidden transition is applied.
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- PAR ID:
- 10654095
- Publisher / Repository:
- Wiley
- Date Published:
- Journal Name:
- Advanced Materials
- ISSN:
- 0935-9648
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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