Photoswitch generation using mechanical force

Abstract

The field of polymer mechanochem. investigates the use of mech. force to promote selective chem. transformations. Polymer chains transduce external mech. forces to a particular covalent bond in mech. sensitive mols. called mechanophores, resulting in a specific chem. reaction. We report on a new mechanophore based on a cyclopentadienemaleimide Diels-Alder adduct that undergoes a retro-[4+2] cycloaddn. reaction promoted by mech. force to reveal a diarylethene (DAE) photoswitch. Initially, the mechanophore is photochem. inert because it does not possess the necessary 6p electronic framework required for electocyclization; however, ultrasound-induced mech. activation of the mechanophore covalently linked to polymer chains generates a DAE photoswitch, which isomerizes between colorless and colored forms upon exposure to UV and visible light. Control expts. confirm the mech. origin of the revealed photochromic activity and illustrate the thermal stability and reversible switching properties of the cyclopentadiene-based DAE photoswitch.