Unveiling Intermolecular Frustrated Lewis Pairs in Single-Molecule Junctions

Area of Science:

• Molecular Electronics and Supramolecular Chemistry
• Single-Molecule Studies of Noncovalent Interactions

Background:

• Intermolecular frustrated Lewis pairs (FLPs) are crucial in catalysis but difficult to study at the single-molecule level due to their transient nature.
• Existing methods struggle to detect the ultralow interaction energies and transient dynamics of FLPs, hindering mechanistic understanding of weak orbital coupling.

Purpose of the Study:

• To develop a method for detecting and characterizing frustrated Lewis pairs (FLPs) at the single-molecule scale.
• To utilize single-molecule conductance as a sensitive probe for weak orbital perturbations and noncovalent interactions.

Main Methods:

• Engineering a sterically hindered molecular probe (OPE-Py-M) capable of forming stable in situ FLP adducts.
• Utilizing scanning tunneling microscopy break junction (STM-BJ) techniques to form and measure single-molecule electrical junctions.
• Validating FLP formation through Nuclear Magnetic Resonance (NMR) spectroscopy and UV-Visible (UV-Vis) charge-transfer band analysis.

Main Results:

• Stable frustrated Lewis pair (FLP) adducts were successfully formed within single-molecule junctions.
• A quantifiable conductance attenuation (from 10^-4.39 to 10^-4.78 G₀) was observed upon FLP formation, indicating electronic perturbation.
• NMR upfield shifts and UV-Vis charge-transfer bands corroborated the formation and electronic changes associated with FLPs.

Conclusions:

• Single-molecule conductance measurements provide an ultrasensitive platform for detecting orbital perturbations below hydrogen-bond energy thresholds.
• This technique enables unprecedented investigation of noncovalent interactions, including FLPs, in molecular electronics.
• The study opens new avenues for understanding and designing self-assembled molecular systems and catalytic processes.