The Mechanism of Flex‐Activation in Mechanophores Revealed By Quantum Chemistry

Abstract

Flex‐activated mechanophores can be used for small‐molecule release in polymers under tension by rupture of covalent bonds that are orthogonal to the polymer main chain. Using static and dynamic quantum chemical methods, we here juxtapose three different mechanical deformation modes in flex‐activated mechanophores (end‐to‐end stretching, direct pulling of the scissile bonds, bond angle bendings) with the aim of proposing ways to optimize the efficiency of flex‐activation in experiments. It is found that end‐to‐end stretching, which is a traditional approach to activate mechanophores in polymers, does not trigger flex‐activation, whereas direct pulling of the scissile bonds or displacement of adjacent bond angles are efficient methods to achieve this goal. Based on the structural, energetic and electronic effects responsible for these observations, we propose ways of weakening the scissile bonds experimentally to increase the efficiency of flex‐activation.

The Activation Efficiency of Mechanophores Can Be Modulated by Adjacent Polymer Composition

“…This paves the way for a fine-tuning of the activation rate of mechanophores in polymers when exposed to mechanical deformation or ultrasound, with the possibility to either maximize mechanophore activation or suppress it below a threshold force. In the future, we plan to apply our findings to maximize the efficiency of flex-activation of mechanophores in polymers, [31][32][33] which can be used for the release of small molecules. Moreover, it is planned to apply quantum chemical models of pressure [34] to test the role of the linkers in experiments in which mechanophore activation is achieved by compression.…”

A Two-Step Baromechanical Cycle for Repeated Activation and Deactivation of Mechanophores

“…Within the past two decades, mechanical force has emerged as a sustainable alternative to more traditional means of activating chemical reactions. , At the focal point of many experimental and computational mechanochemical studies are mechanophores, that is, small molecular units that are typically incorporated into the backbones of polymers. − Mechanochemical deformation triggers profound structural rearrangements in the mechanophore, for example, bond rupture. This effect has been used in the development of force-responsive and stress-sensing materials, , as well as for triggering reaction cascades , and the release of small molecules. , However, force-induced structural changes in mechanophores are typically permanent. While some reversible mechanophores have been reported, the fact that most mechanophores cannot easily be reverted back to their deactivated form limits the applicability of force-responsive materials in everyday applications because of their limited recyclability.…”

“…This effect has been used in the development of force-responsive and stress-sensing materials, 6,7 as well as for triggering reaction cascades 8,9 and the release of small molecules. 10,11 However, force-induced structural changes in mechanophores are typically permanent. While some reversible mechanophores have been reported, 12 the fact that most mechanophores cannot easily be reverted back to their deactivated form limits the applicability of force-responsive materials in everyday applications because of their limited recyclability.…”

The activation efficiency of mechanophores can be modulated by adjacent polymer composition

“…This paves the way for a ne-tuning of the activation rate of mechanophores in polymers when exposed to mechanical deformation or ultrasound, with the possibility to either maximize mechanophore activation or to suppress it below a threshold force. In the future, we plan to apply our ndings to maximize the efficiency of ex-activation of mechanophores in polymers, [32][33][34] which can be used for the release of small molecules. Moreover, it is planned to apply quantum chemical models of pressure [35][36][37][38][39][40][41][42] to test the role of the linkers in experiments in which mechanophore activation is achieved by compression.…”