Anthracene dimer crosslinked polyurethanes as mechanoluminescent polymeric materials

Mechanoluminescent polymers release energy in the form of light under mechanical stimuli at an intensity proportional to the applied mechanical stress. Anthracene compounds, which can photo-dimerize to form non-fluorescent dimers under 365 nm UV light irradiation and recover to fluorescent monomers via heating or UV light of 254 nm, are good candidates for research on mechanoluminescent polymeric materials in dynamic covalent systems. In this work, anthracene-tailored trifunctionalized polyurethane (PU) prepolymers were synthesized, and these prepolymers formed crosslinked structures via the dimerization of anthracene groups under UV irradiation. It was found that blue fluorescence was observed when these anthracene dimer crosslinked materials were pressed or scratched, indicating that the dynamic dimer structure was destroyed by external force. 1H NMR investigation confirmed the formation of anthracene monomers after the mechanical experiments. Furthermore, the fluorescence intensity increased with the increasing pressure applied to the PU materials, suggesting that the formation of anthracene monomers was closely related to the external force. These anthracene dimer crosslinked PU materials can provide a new avenue for fluorescent mechanosensitive materials.