Mechanically Triggered Multicolor Fluorescence Switching via Distance-Dependent FRET Effect

Mechanoluminescent polymers capable of fluorescence modulation have attracted considerable interest for applications in stress-sensing and flexible electronics. Though Förster resonance energy transfer (FRET) has proven to be an effective mechanism for generating mechanoresponsive fluorescence changes, current systems predominantly depend on force-induced structural changes in chromophores. Herein, we report a mechanofluorochromic strategy exploiting force-modulated distance control between a FRET pair. A furan-maleimide Diels-Alder (DA) adduct covalently linked to pyrene (donor) and dansylamide (acceptor) was designed and incorporated at the midpoint of poly(methyl acrylate) (PMA) chains. Mechanical cleavage of the adduct spatially separates the FRET pair, effectively abolishing energy transfer and concurrently activating photoinduced electron transfer (PET). In acetonitrile, ultrasonication shifted the fluorescence from yellow to high-quality white light. Through changing the solvents, we demonstrate programmable multicolor switching. In toluene, the fluorescence evolves from green to cyan, while in DMF, rapid activation induced a transition from yellow to white emission. Each solvent system exhibits unique kinetic trajectories, enabling precise control over the chromatic response. This work demonstrates that controlled modulation of the FRET distance provides a versatile strategy for developing smart, multicolor mechanoluminescent materials without the need for a complex system design.