Controlling Solid-State Mechanochemical Pathways in Triarylmethane Mechanophores via Molecular and Matrix Design

Controlling reaction pathways under mechanical force is a challenge in polymer mechanochemistry. Most mechanophores exhibit a single dissociation route, and examples of mechanistic multiplicity are exceedingly rareparticularly in the solid state. Here, we report triarylmethane mechanophores that enable predominant homolytic or heterolytic pathways in polymer networks through combined molecular and matrix design. Two variants were synthesized: Tr-1, bearing a benzyl ether leaving group connected through a weak C-O bond, and Tr-2, incorporating a cyanoacetate leaving group linked via a weak C-C bond. Embedded in poly-(methyl acrylate) (PMA) and poly-(methyl acrylate-co-2-hydroxylethyl acrylate) (P-(MA-co-HEA)) networks, these mechanophores display mechanochromic responses that report distinct cleavage mechanisms. Tr-1 undergoes homolysis in PMA, while hydrogen-bond donors in P-(MA-co-HEA) promote heterolysis. Tr-2 favors heterolytic dissociation regardless of matrix composition, instead. Optical measurements, EPR spectroscopy, and DFT calculations support these assignments and further establish triarylmethane ethers as mechanochemical probes of hydrogen bond donors.