Triarylmethane Mechanophores Enable Full-Visible Spectrum Mechanochromism

Covalent mechanophores are molecular motifs that contain weak bonds, which are preferentially cleaved in response to the application of a mechanical force. Specially designed motifs can signal such bond scission events by changing their optical absorption or emission characteristics and thus exhibit mechanochromism. Here, we report the synthesis of three triarylmethane benzyl ether derivatives and their use as mechanochromic cross-linkers in elastomeric networks. Mechanical stimulation of these polymers triggers the heterolytic cleavage of the C-O ether bond of the triarylmethanes, which leads to the formation of resonance-stabilized carbocations that absorb light in the visible range. The materials adopt blue, yellow, or red coloration depending on the chemical design of the triarylmethane mechanophore. The color palette can be further expanded by simple combinations of these three colors. Thus, our work demonstrates the versatility of the triarylmethane platform in polymer mechanochemistry.