Multi‐Level Waterproofing Strategy Toward an Ultra‐Water‐Stable 2D Luminescent Copper(I) Iodide: From Atomic‐Level Passivation to Surface‐Interface Hydrophobicity

Abstract Organic–inorganic hybrid materials face significant barriers to large‐scale commercialization, primarily stemming from their intrinsic vulnerability to moisture‐triggered hydrolytic degradation. Herein, an ultra‐stable 2D copper(I) iodide, Cu 6 I 6 (26dmpz) 3 , is engineered through a synergistic waterproofing strategy that integrates atomic‐level passivation and surface‐interface hydrophobicity. N‐metal coordination in Cu 6 I 6 (26dmpz) 3 (26dmpz = 2,6‐dimethylpyrazine) passivates H‐bond donors at atomic‐level, blocking hydrolytic degradation induced by N─H···O interactions. Its methyl‐dominated non‐polar surface and “hydrogen‐bond‐free” contribute to low surface energy (37.68 mJ m −2 ) and polarity (4.09 mJ m −2 ), minimizing water adsorption, as corroborated by a 130.8° contact angle. The 2D corrugated groove structure creates a physical barrier against water penetration at solid–liquid interfaces. This endows Cu 6 I 6 (26dmpz) 3 with exceptional water stability, preserving its structure and luminescence after 30 days in water. Moreover, it shows bright orange–red emission (616 nm) with strong blue‐light response, attributed to halide/metal‐to‐ligand charge transfer. The fabricated white LED exhibits an ultra‐high color rendering index (CRI = 89.9), showing tremendous potential for high‐quality solid‐state lighting.