A Thermally Stable and Processable [4+2] Photodimer of π-Extended Anthracene as Optical Force Probe for Damage Detection in Thermoplastics

Mechanophores that translate mechanical force into optical signals are powerful tools for probing damage in polymeric materials, yet regularly suffer from undesired thermal reactivity compromising mechanochemical selectivity and processability of the host polymer. Here, we show that the [4+2] photodimerization of highly emissive 9-π-extended anthracene yields an optical force probe (OFP) which features excellent thermal stability above 200 °C as well as photochemical robustness. We demonstrate mechanochemical activation in thermoplastic polymers using blends of commercial poly(methyl methacrylate) (PMMA), polystyrene (PS), thermoplastic polyurethane (TPU), and polyethylene (PE) at low functional material loadings (≤ 5 wt%). Importantly, we subject OFP-functionalized TPU to melt processing including extrusion and melt spinning, and obtain mechanofluorogenic fibers that retain intact OFPs. Together, our results underscore photodimerization of fluorophores as strategy to tailor the optical readout of OFPs and open an avenue to investigate molecular-level damage in melt-processed thermoplastics.