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-phenyleneethynylene unit extended the π-conjugation. The polyurethanes absorbed light at 402 nm and fluoresce at 477 nm in the solution state. Stretching the polymer films under UV light leads to a photoluminescent 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 of aggregation degree of the naphthalimide moieties.