The mechanochemical properties of synthetic molecules have been studied using single-molecule techniques such as atomic force microscopy (AFM) or optical tweezers. Here we present recent AFM-based single-molecule force spectroscopy (SMFS) investigations on functional molecules, and further discuss on ongoing research in our group.<br/><br/>Mechanically interlocked molecules (MIMs), such as rotaxanes, catenanes and molecular knots, have attracted a lot of attention in the past years for the design of artificial molecular machines. Unique properties can arise from these molecules, originating from the presence of mechanical bonds in their architectures. Their use as molecular switches, machines, or motors has been intensively discussed recently.<br/><br/>We will first focus on the mechanical stretching of individual MIMs in solution. In recent works, we evidenced remarkable force performances and fast dynamics of such artificial molecules compared to their natural analogs. Additionally, we will describe the first example of AFM-based pulling experiments on artificial molecular knots at the single-molecule level. The synthesis of a trefoil knot —the simplest prime knot— was modified to facilitate its interfacing for AFM experiments. Standard SMFS experiments on individual knots showed typical force deviations from the usual force-extension curves of flexible polymers, and a precise tightening process was evidenced. Such challenging studies are essential to understand the impact of mechanical bonds on the properties of wholly synthetic architectures and are crucial for further uses of MIMs in the design of functional materials or other applications.

Employing single-molecule techniques to quantify the performance of small synthetic molecules

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ACS Fall 2022

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