# Template‐Controlled Mechanochemical Dissociation of a Rotaxane

## TL;DR

This paper shows how a single Pd atom can control how a rotaxane breaks apart under force, enabling different mechanical responses in materials.

## Contribution

The study demonstrates selective control over mechanochemical dissociation pathways in a rotaxane by manipulating a Pd template.

## Key findings

- Presence of a Pd atom favors unstoppering pathway in rotaxane dissociation.
- Removal of the Pd atom increases macrocycle flexibility, enabling dethreading pathway.
- This control allows for tunable mechanical responses in potential materials.

## Abstract

The mechanochemical dissociation of rotaxanes has been used in the design of materials with the ability to dissipate energy and of force‐controlled release systems. The former takes advantage of the dissociation by dethreading, a noncovalent process in which the macrocycle is forced over a stopper, while in the latter, the forceful contact between the macrocycle and stopper provokes the rupture of a covalent bond and release of the stoppering unit. As the dissociation pathway is dictated by the relative size of the macrocycle and the stopper, a rotaxane under tension can usually only undergo one of these two pathways. However, the ability to control the mechanochemical reactivity of a rotaxane in situ would allow the creation of multiresponsive materials. Here, we show how to selectively access unstoppering and dethreading pathways from the same rotaxane structure by respectively keeping or removing a single Pd atom to alter the size of the cavity of the macrocycle in a rotaxane built around a PdII template. We anticipate that these findings will have applications in the design of force‐responsive materials and devices in which the mechanical response can be tuned to suit specific uses.

The presence or absence of the Pd template used in rotaxane formation selectively leads to two different mechanochemical dissociation pathways. The Pd maintains a smaller cavity size that favors dissociation by unstoppering. Removal of the Pd template atoms increases the size and flexibility of the macrocycle, which allows for disassembly by dethreading. The ability to selectively switch the mechanochemical behavior of rotaxanes could be used to control the mechanical properties of polymer materials.