Ultra‐Stable Luminescent Smart Textiles Embedded With Thermally Responsive Copper Iodide Clusters

Copper iodide clusters have emerged as a promising candidate for flexible optoelectronic devices due to their structural versatility and exceptional photoluminescence (PL) properties, yet their practical application is hindered by insufficient mechanical fragility and environmental stability. Herein, a scalable wet‐spinning strategy is presented to fabricate ultrastable Cu 4 I 4 (L) 4 @CA fibers (L 1 = 4‐benzylpyridine; L 2 = 4‐tert‐butylpyridine; CA = calcium alginate). The molecular encapsulation preserves high photoluminescence quantum yields (PLQYs >85%) at an ultralow 1 wt% doping while enabling fully reversible thermochromic switching: white to yellow (L 1 ) and blue–purple to orange (L 2 ) transitions across 80–300 K. The fibers demonstrate textile‐grade flexibility and ultrahigh environmental stability (>98% PL retention under humidity/UV/solvents). Leveraging these properties, a dual‐authentication encryption platform is pioneered featuring triple‐state information switching (ambient, UV, and cryogenic states) and DNA‐inspired binary photonic encoding using programmable Y‐/cross‐shaped spinnerets for data transcription. By harmonizing stimuli‐responsive optoelectronics with textile processability, this work establishes a synergistic material platform for next‐generation secure wearables, stealth luminescent textiles, and hierarchical anti‐counterfeiting systems.