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 (Fact) practically and efficiently.
Identifying a mechanophore’s Fact is a focus of mechanochemistry. As have been done in an existing
framework, we generated the ΔGτ‡–Fτ curve,
where Fτ is the value of external
force and ΔGτ‡ denotes the force-coupled free energy barrier of a specific reaction
under Fτ. Such a curve is then used
to determine the Fact of a certain mechanophore
when combined with the Eyring equation. Although generating such a
ΔGτ‡–Fτ 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.