This photoactivity change provides a convenient readout to monitor the ultrasound-mediated mechanochemical activation of PMA1-PMA3 by measuring their photostationary-state absorbance with UV-vis spectroscopy (Figure ). A polymer solution was subjected to standard ultrasonication conditions, and aliquots of the solution were removed and analyzed after each duration of ultrasonication. All initial polymer solutions containing the parallel diarylethene mechanophores were colorless and photoinert. Exposing the sonicated solutions to UV irradiation (λ = 365 nm) leads to the development of a red color due to the photo-excitation of converted mechanophores, with an absorption peak at around 510-530 nm. Their photostationary- state absorptions were measured as a function of ultrasonication time, with PMA3 shown in Figure as a representative example (Figure ). Their peak absorbance values in the visible region were used to calculate the percentage mechanochemical conversion. By fitting the ultrasonication-dependent conversion to a first-order rate expression (Figure and Figure ), the rate constants of the pseudo-first-order sonomechanical reactions are calculated to be 0.105 ± 0.003 min -1 , 0.145 ± 0.003 min -1 , and 0.239 ± 0.007 min -1 for PMA1-PMA3, respectively. The trend of these sonomechanical activation rates is consistent with the mechanosensitivity trend among M1-M3 observed in our SMFS and CoGEF results, collectively supporting the lever-arm SMAR hypothesis.