Mechanical gating of a mechanochemical reaction cascade

Abstract

Covalent polymer mechanochemistry offers promising opportunities for the control and engineering of reactivity. To date, covalent mechanochemistry has largely been limited to individual reactions, but it also presents potential for intricate reaction systems and feedback loops. Here we report a molecular architecture, in which a cyclobutane mechanophore functions as a gate to regulate the activation of a second mechanophore, dichlorocyclopropane, resulting in a mechanochemical cascade reaction. Single-molecule force spectroscopy, pulsed ultrasonication experiments and DFT-level calculations support gating and indicate that extra force of >0.5 nN needs to be applied to a polymer of gated gDCC than of free gDCC for the mechanochemical isomerization gDCC to proceed at equal rate. The gating concept provides a mechanism by which to regulate stress-responsive behaviours, such as load-strengthening and mechanochromism, in future materials designs.

A single‐molecule reaction cascade: First‐principles molecular dynamics simulation

“…In eight out of nine ground‐state simulations for system 1 , the formation of the EZ isomer was observed as expected . In the ninth simulation, in which the lower pulling velocity was used, the ZZ isomer was formed.…”

“…To conclude, the authors succeeded to synthesize a very valuable system which is able to work as a reaction cascade and it is highly exciting how organic synthesis now meets mechanochemistry.…”

“…Normally, the LSD formalism (local spin density formalism, also called unrestricted Kohn–Sham theory, UKS) must be applied, which allows electrons to be paired or unpaired, whatever is energetically favorable. In the present article, both approaches are applied to a system recently designed by Wang et al, see also Ref. [ ].…”

“…The authors succeeded to demonstrate that the polymer they synthesized can be used in mechanical reaction gating. The article already contains a thorough theoretical treatment. The present article adds a molecular dynamics treatment to elucidate the reaction mechanisms and possibly the stereochemistry.…”

The Challenges and Opportunities of Contemporary Polymer Mechanochemistry

“…[21,22] This focus on quantitative molecular interpretation of mechanochemical behavior of polymers is less than ad ecade old and regrettably remains somewhat of an iche of contemporary mechanochemistry.F or most of its history,t he field studied primarily fragmentations of simple commodity (e.g.,p olystyrene, polyamides) or biological (DNA,polysaccharides) polymers. These data are routinelyf itted to empirical models that postulate ac ertain relationship (often simple proportionality) between the applied force and lowering of the apparent kinetic barrier.…”