Mechanochemical Activation of Spiropyran in PMMA - A Hybrid Quantum Chemical/Atomistic/Coarse-Grained Approach

Embedding mechanophores into polymer matrices to activate mechanochemical reactions has been extensively employed to realize diverse functional applications. Spiropyran (SP) is a widely used mechanophore that undergoes force-induced isomerization into its activated merocyanine (MC) form, accompanied by a color change. To accurately simulate the SP-MC isomerization process under tension, the present work introduces a large-scale hybrid coarse-grained/atomistic (CG/AA) model in which poly(methyl metacrylate) (PMMA) monomers are represented by in dividual beads, while SP remains fully described at the AA level. We used force field parameters derived from quantum chemical (QC) data, employing the fully atomistic framework previously developed by our group. The underlying CG PMMA force field was reparameterized to match experimental bulk properties and compared with a corresponding atomistic force field. This approach enabled deformation simulations of significantly larger systems than possible with a pure AA force field, at reduced computational cost, thereby providing novel insights into force transduction and mechanophore activation. Furthermore, a parabolic stress distribution was observed along individual PMMA chains, resulting in preferential SP activation near chain centers. Non specific chain scission events occurred far less frequently than SP activations. The developed hybrid model offers a powerful framework for investigating more complex mechanophore doped polymer networks.