Amplification of spiropyran mechanophore activation in bulk polymers through a tethering strategy†

The insertion of force-active molecules (mechanophores) with optical-switching properties into polymer chains has enabled the development of various mechanochromic polymers. Among them, colorimetric spiropyran (SP) has been the most extensively studied. However, the low extent of SP activation in bulk materials and the associated poor material mechano-sensitivity have hindered its broader applications. To address this challenge, we report the amplification of SP mechanophore activation in bulk materials through a tethering design. Two SP mechanophores were tethered through a long aliphatic linker, and the resulting molecule was employed as a crosslinker in silicone elastomer networks. This approach resulted in an enhancement of SP activation by more than twofold compared to its mono-SP counterpart. Additionally, we observed that increasing the number of added short linkers leads to greater tension constraints on these linkers, creating a self-reinforcing effect on mechanophore activation. We anticipate that this tethering strategy can be adapted to other non-scissile mechanophores in bulk studies.