Caged AIEgens: Multicolor\nand White Emission Triggered\nby Mechanical Activation

Aggregation-induced emission luminogens (AIEgens) that\nrespond\nto mechanical force are increasingly used as force probes, memory\ndevices, and advanced security systems. Most of the known mechanisms\nto modulate mechanoresponsive AIEgens have been based on changes in\naggregation states, involving only physical alterations. Instances\nthat employ covalent bond cleavage are still rare. We have developed\na novel mechanochemical uncaging strategy to unveil AIEgens with diverse\nemission characteristics using engineered norborn-2-en-7-one (NEO)\nmechanophores. These <b>NEO</b> mechanophores were covalently\nintegrated into polymer molecules and activated in both the solution\nand solid states. This activation resulted in highly tunable fluorescence\nupon immobilization through solidification or aggregation, producing\nblue, green, yellow, and orange-red emissions. By designing the caged\nand uncaged forms as donor–acceptor pairs for Förster\nresonance energy transfer (FRET), we achieved multicolor mechanofluorescence,\neffectively broadening the color spectrum to include white emission.\nAdditionally, we computationally explored the electronic structures\nof activated NEOs, providing insights into the observed regiochemical\neffects of the substituents. This understanding, together with the\nnovel luminogenic characteristics of the caged and activated species,\nprovides a highly tunable reporter that traces progress with continuous\ncolor evolution. This advancement paves the way for future applications\nof mechanoresponsive materials in areas like damage detection and\nbioimaging.