A Two-Step Baro-Mechanical Cycle for Repeated Activation and Deactivation of Mechanophores

Mechanophores that are embedded in a polymer backbone respond to the application of mechanical stretching forces by geometric changes such as bond rupture. Typically, these structural changes are irreversible, which limits the applicability of functional materials that incorporate mechanophores. Using computational methods, we here present a general method of restoring a force-activated mechanophore to its deactivated form by using hydrostatic pressure. We use the well-known spiropyran-merocyanine (SP-MC) interconversion to show that repeated activation and deactivation of the SP mechanophore can be achieved by alternating application of mechanical stretching forces and hydrostatic compression. In the baro-mechanical cycle, MC plays the role of a “barophore” that responds to hydrostatic pressure by bond formation. The activation and deactivation pathways of SP and MC are understood in terms of strain and electronic effects. Beneficially, this two-step baro-mechanical cycle can be observed in real time by using UV/Vis spectroscopy. Our calculations pave the way for massively improving the applicability and reusability of force-responsive materials.