A Two-Step Baromechanical 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 incorporating
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 spiropyran-merocyanine
(SP-MC) interconversion to show that repeated activation of the SP
mechanophore and deactivation of MC can be achieved by alternating
mechanical stretching and hydrostatic compression, respectively. In
the baromechanical cycle, MC acts as a “barophore” that
responds to hydrostatic pressure by bond formation. The activation
and deactivation of SP/MC are understood in terms of strain and electronic
effects. Beneficially, this two-step baromechanical cycle can be observed
in real time by using UV/vis spectroscopy. Our calculations pave the
way for improving the applicability and reusability of force-responsive
materials.