Extension of the spiropyran molecule, Figure (a), can induce the scission of the C-O bond at the spiro atom through an isomerization reaction that results in a chromatic response, as shown in Ref. 4. As was done in prior studies of mechanophores , we performed CoGEF simulations to characterize this reaction but, in addition to the constraints applied to the anchor H atoms, we apply MB-SMD around a central bond marked with yellow in Fig. . The associated dihedral has an equilibrium value of 72 and ten independent CoGEF simulations were performed for target torsional angles ranging from 70 to 25.