A Thermally and Photochemically Stable Fluorescent Radical-type Mechanophore for Durable Mechanoresponsive Polymers

The development of mechanophores
has opened new avenues in the
design of functional materials; however, most reported mechanophores
rely on thermally or photochemically labile bonds, which limits their
stability under practical conditions. Herein, we report diarylacetonitrile-α-carboxylic
ester (DAANAC) as a robust radical-type mechanophore (RM) that is
inert to both thermal and photochemical stimuli. DAANAC exhibits remarkable
stability upon heating above 200 °C and demonstrates excellent
photostability under UV irradiation at 365 and 254 nm. In contrast,
DAANAC generates fluorescent diarylacetonitrile radicals upon mechanical
activation, such as grinding or stretching, when incorporated into
linear or cross-linked polymers. Tensile tests of DAANAC-cross-linked
elastomers show strain-induced fluorescence and stress–strain
behavior comparable to that of the control elastomer without mechanophores,
underscoring its ability to visualize mechanical damage without compromising
mechanical properties. These findings establish DAANAC as a unique
fluorescent RM that bridges the gap between force responsiveness and
structural robustness, expanding the design space for durable mechanoresponsive
polymers.