Enhancing the Fluorescence of an Aggregation‐Induced Emission‐Active Polymorphic System With Remarkable Mechanochromism for Visualizing Microcracks and Stress Distribution in Textiles

ABSTRACT Visualization of microcracks and stress distribution is crucial for material usability and safety assessment, yet effective monitoring technologies remain very limited. In this work, an organic luminogen TPEXD with aggregation‐induced emission (AIE) properties has been developed by introducing a 3,4,5,6,7,9‐hexahydro‐1 H ‐xanthene‐1,8(2 H )‐dione group onto tetraphenylethylene via a nonconjugated methylene linkage. TPEXD forms two polymorphs: a deep‐blue fluorescent crystal SCb with a low photoluminescence quantum yield ( Φ PL ) of 2.4% and a blue fluorescent crystal SCc with a high Φ PL of 22.6%. Notably, SCb exhibits remarkable mechanochromism (MC) properties and force‐induced emission enhancement (FIEE) characteristics opposite to classical mechano‐responsive AIE materials, with the Φ PL increasing to 30.1% under external force. SCb integrates three mechano‐responsive properties, including MC, FIEE, and mechanoluminescence (ML). Under pressure increased from 0 to 17.33 GPa, the emission maximum of SCb gradually red‐shifts by 106 nm. Inspired by the MC and FIEE properties, the SCb were leveraged for inkless writing, impact indication, visualized monitoring of microcracks, and stress distribution in textiles. This work provides helpful guidance for developing AIE materials with MC and FIEE characteristics and offers a practical approach for the visualized monitoring of microcracks and stress distribution in materials.