Single-molecule observation of mechanical isomerization of spirothiopyran and subsequent Click addition

Spirothiopyran (STP) is particularly attractive when used as a mechanophore to endow polymers with both damage-signaling and self-reinforcing capacity. It is, however, not clear the actual force required to induce the cycloreversion of STP into ring-opened thiomerocyanine (TMC), which reacts spontaneously with activated C-C bonds. Here, we used atomic force microscopy (AFM)-based single molecule force spectroscopy (SMFS) to study the mechanochemistry of STP mechanophore. It is found that the ring-opening of STP at room temperature requires forces of ∼ 200–400 pN, depending on the pulling speed. In addition, the reversibility of STP to TMC isomerization is demonstrated. Finally, mechanochemically induced intermolecular Click addition is achieved in single molecule level by pulling STP in the presence of maleimide.