Simple tool could facilitate discovery of new mechanically-responsive materials

The exploration of mechanophores continues to expand the practical application of these molecules in materials science, organic synthesis, and pharmaceuticals due to their ability to change physically or chemically in response to force.

A mechanophore discovered a few years ago by University of Illinois Urbana-Champaign chemists, including Prof. Jeffrey Moore and graduate student Yunyan Sun, can release controlled amounts of carbon monoxide when triggered by mechanical force, which can potentially be used in the human body as a drug to treat diseases and conditions.

Called NEO, it depends on the breaking of carbon-carbon bonds, which is common in a variety of mechanochemical transformations. But a major challenge in studying mechanophores is understanding and predicting the reactivity of breaking the C–C bond.

Typically, that requires a lot of experimentation and calculation due to the unpredictable vectoral nature of forces like pushing or pulling.

A research team that includes Moore and Sun and researchers at MIT and Duke University has developed a simple and intuitive tool that can predict without lengthy experimentation and calculation the reactivity of C–C bonds when designing mechanophores.

Their paper, "The Tension Activated Carbon-Carbon Bond," published in the journal Chem, explains their work on this tool, which reports a new computational model and its experimental validation.

According to the researchers, this tool could ultimately lead to the discovery of new mechanically-responsive materials and enhance understanding of structure-reactivity relationships, leading to advancements in the field of mechanochemistry.

Sun said the tool is derived from the Morse Potential, an interatomic interaction model for the potential energy of a diatomic molecule and a classic chemistry model familiar to freshman level college students.

"It's very, very simple derivation. Everyone can do it," Sun said of this mnemonic tool, called the tension model of bond activation (TMBA).

By constructing the restoring force triangle, TMBA captures the mechanochemical activation of C–C bonds in complex molecules using two easily computed parameters—effective force constant and reaction energy—as the key molecular features that govern mechanochemical kinetics.

Their triangle helps make sense of complex computations, transforming the results into useful information.

"These calculations are quantitatively accurate but difficult to intuit. Our triangle is a way to find molecular features and insight from the results, and therefore gain a better understanding of what this computational model is telling you," Moore explained.

Sun said providing an intuitive tool like this is very important.

"There are always high-level complicated computations that can help you to some extent predict and understand things, but in most cases it's not super helpful to start with those. You need something that's intuitive and simple to help you, to help guide you designing mechanophores. Our model really helps you understand what's going on with the complicated calculations, but you just see the results," Sun said.