Mechanochromic polyurethane elastomers containing main-chain naphthalimide moieties

Abstract

Novel mechanochromic polyurethane elastomers were synthesized using naphthalimide as a mechanofluorophore. Connection of two naphthalimide units with an ethynylene–phenylene–ethynylene unit extended the π-conjugation. The polyurethanes absorbed light at 402 nm and fluoresced at 477 nm in the solution state. Stretching the polymer films under UV light induces a photoluminescence color change from green to blue, which is attributed to the increased intermolecular distance between naphthalimide units. Quantum mechanical calculations and molecular dynamics simulations supported the assumption that the mechanochromism is caused by the change in aggregation degree of the naphthalimide moieties.