Exploiting force sensitive spiropyrans as molecular level probes

Spiropyran (SP) mechanophore was synthesized into the soft or hard phase of segmented polyurethanes (SPU) and used as a molecular probe of force and orientation. Upon either tensile stretching or irradiation with UV light the SP-linked segmented polyurethane (SP-SPU) adopt a deep purple coloration and are fluorescent, demonstrating the force and UV-induced formation of the open merocyanine (MC) form of the mechanophore. Order parameters calculated from the anisotropy of the fluorescence polarization of merocyanine (MC) were used to characterize the orientation in each phase. Exploiting the ability of SP to be force activated, the SP-SPUs were also mechanically activated to track the force and orientation in each domain of segmented polyurethane during uniaxial tensile loading.