Designing Heterolytic and Homolytic Bond Scission in Diarylmethane Mechanophores.

Mechanical force can often unlock chemical reactivity inaccessible under conventional conditions. However, understanding how molecular structure and environment govern mechanochemical reaction pathways in the solid state remains a significant challenge. In particular, establishing design principles to access heterolytic bond scission in nonpolar materials remains elusive. Here, we investigate a family of diarylmethane-based mechanophores embedded in polymer networks to elucidate how bond identity, substituent electronics, leaving-group stabilization, and matrix interactions collectively determine mechanochemical reactivity. By systematically varying the nature of the scissile bond (C-O vs C-C), the electronic properties of the diarylmethane core, and the presence or absence of hydrogen-bonding functionalities in the surrounding polymer matrix, we establish structure-reactivity relationships that govern the formation of radical and ionic species under tensile load. Mechanophores containing C-O bonds display environment-dependent behavior, with homolytic cleavage dominating in non-hydrogen-bonding matrices and heterolytic scission accessible only when both strongly donating substituents and hydrogen-bond donors are present. In contrast, mechanophores incorporating polarized C-C bonds with strongly stabilizing leaving groups undergo heterolytic cleavage to yield diarylcarbenium ions, even in matrices lacking hydrogen-bonding functionality. These results establish design principles linking molecular structure and polymer environment to mechanochemical reactivity and demonstrate that ionic pathways can be accessed and stabilized in the solid state. More broadly, this work provides guidelines for designing mechanoresponsive materials with distinct reaction pathways and mechanochromic responses.