Mechanical Reactivity of Two Different Spiropyran Mechanophores in Polydimethylsiloxane

We investigate the effect of pulling point location on the mechanochemical activation of two isomers of spiropyran in cross-linked polymeric materials through computational calculations and in situ fluorescence measurements. The threshold stress and strain required to activate the spiropyran mechanophores under tensile load are characterized. For both spiropyran isomers, applied stress favors the activated merocyanine states; however, despite differences in mechanochemical behavior predicted by quantum chemical calculations and previous single molecule experiments, both spiropyran isomers exhibit similar mechanochemical reactivity in bulk polymeric materials. The kinetics of the spiropyran-merocyanine transition under different tensile stresses are also examined. Overall, we find that varying the pulling geometry on the spiropyran mechanophore has only a minimal effect on the mechanical activation in bulk polymeric materials due to the complex nature of the macroscopic system.