Abstract
The hydrogen bond represents a fundamental interaction widely existing in nature, which plays a key role in chemical, physical and biochemical processes. However, hydrogen bond dynamics at the molecular level are extremely difficult to directly investigate. Here, in this work we address direct electrical measurements of hydrogen bond dynamics at the single-molecule and single-event level on the basis of the platform of molecular nanocircuits, where a quadrupolar hydrogen bonding system is covalently incorporated into graphene point contacts to build stable supramolecule-assembled single-molecule junctions. The dynamics of individual hydrogen bonds in different solvents at different temperatures are studied in combination with density functional theory. Both experimental and theoretical results consistently show a multimodal distribution, stemming from the stochastic rearrangement of the hydrogen bond structure mainly through intermolecular proton transfer and lactam–lactim tautomerism. This work demonstrates an approach of probing hydrogen bond dynamics with single-bond resolution, making an important contribution to broad fields beyond supramolecular chemistry.
Highlights
The hydrogen bond represents a fundamental interaction widely existing in nature, which plays a key role in chemical, physical and biochemical processes
Until now these dynamic processes still remain poorly understood at the single-molecule level because hydrogen bond dynamics under normal conditions, such as bond rearrangements and hydrogen/proton transfer processes, are extremely difficult to directly probe in solvents
Single-molecule techniques[24,25], in particular graphene electrode-molecule single-molecule junctions (GM-SMJs)[26], are promising because they are able to covalently integrate individual molecular systems tested as the conductive channel into electrical nanocircuits, solving the key issues of the device fabrication difficulty and the poor stability
Summary
The hydrogen bond represents a fundamental interaction widely existing in nature, which plays a key role in chemical, physical and biochemical processes. Single-molecule techniques[24,25], in particular graphene electrode-molecule single-molecule junctions (GM-SMJs)[26], are promising because they are able to covalently integrate individual molecular systems tested as the conductive channel into electrical nanocircuits, solving the key issues of the device fabrication difficulty and the poor stability These techniques prove to be a robust platform of single-molecule electrical detection that is capable of probing the dynamic processes of chemical reactions at the single-event level with high temporal resolution and high signal-to-noise ratios, for example photoinduced conformational transition[27], temperaturedependent σ-bond rotation[28] and host–guest interaction[29]. For the first time we represent direct real-time monitoring of single-molecule hydrogen bond dynamics on the basis of the platform of GM-SMJs, where a quadruple hydrogen bond supramolecular system is covalently sandwiched between graphene point contacts to form stable supramolecule-assembled SMJs
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