Solvent Swelling Activation of a Mechanophore in a Polymer Network

ABSTRACT: A spiropyran mechanophore (force-sensitive molecule), which is fluorescent in its mechanically activated state, is used to investigate swelling-induced mechanochemis-try in cross-linked poly(methyl methacrylate). The spiropyran is incorporated as a cross-linker. A correlation is observed between solvent-induced polymer swelling and fluorescence intensity, suggesting that the forces during swelling are sufficient to drive the electrocyclic ring-opening of spiropyran to its colored and fluorescent merocyanine form. Control experiments and solvatochromic studies validate that activation is indeed due to swelling-induced mechanical forces and not solvent effects. Systematic studies varying solvents and cross-linking densities provide insight into how altering swelling parameters influences the mechanophore response at the molecular level. Solvent swelling is a common process in polymeric materials,