Computational Exploration of Polymer Mechanochemistry: Quantitation of Activation Force and Systematic Discovery of Reaction Sites by the Extended Artificial Force-Induced Reaction Method

A collection of mechanophores was computationally studied using the extended artificial force induced reaction (EX-AFIR) method, which utilizes two different sets of forces to determine the activation force level (<i>F</i>_act) practically and efficiently. Identifying a mechanophore's <i>F</i>_act is a focus of mechanochemistry. As have been done in an existing framework, we generated the Δ<i>G</i>_τ^‡-<i>F</i>_τ curve, where <i>F</i>_τ is the value of external force and Δ<i>G</i>_τ^‡ denotes the force-coupled free energy barrier of a specific reaction under <i>F</i>_τ. Such a curve is then used to determine the <i>F</i>_act of a certain mechanophore when combined with the Eyring equation. Although generating such a Δ<i>G</i>_τ^‡-<i>F</i>_τ curve was tough because locating the force-coupled transition states is time-consuming, the extended AFIR method allowed an efficient exploration of all the relevant transition states on the force-modified potential energy surface (FMPES). The EX-AFIR method was later applied to study the problems encountered in current polymer mechanochemistry research, deriving a concept of "node" which could be used for the design of thermostable mechanophores. The first-ever case study of cubane using EX-AFIR is a vivid example of how the fully automated search of possible reaction pathways on the FMPES is facilitated. Furthermore, it also provided insights into the further design and application of unconventional mechanophores.