Structural Effects on Mechanochemical Reactivity of Anthracene-Maleimide Diels-Alder Adducts

Structure-activity relationship of mechanophores has always been a research focus in the field of polymer mechanochemistry. Here, we report our investigation of the effects of substitution and pulling geometry on the mechanochemical reactivity of anthracene-maleimide Diels-Alder (DA) adducts. The results of both ultrasonication experiments and constrained geometries simulate external force (CoGEF) calculations show that the adducts with the same pulling points at the 9-position of anthracene and the N atom of succinimide but different substituents (e.g., H, alkylthio, or dialkylamino) at the succinimide C2 position can be mechanochemically activated and undergo a retro-DA reaction under applied force with similar reactivity, implying that substitution in the succinimide C2 position has an insignificant effect on the mechanochemical reactivity. Remarkably, the adduct with one of the pulling points changed from the N atom to the C2 substituent of the succinimide becomes mechanochemically inert due to weak mechanochemical coupling associated with poor orientational alignment between the "scissile" bond and the pulling vector.