Copper Halide Hybrids Driven by Irreversible Structural Transitions for Anti-Counterfeiting and Traceability.

The growing demand for high-security anticounterfeiting and traceable information encryption materials requires systems capable of generating irreversible "access records" to prevent replication and tampering. Conventional fluorescent materials, such as organic dyes and rare-earth compounds, are limited by complex synthesis, low luminescence efficiency, and reversible response behaviors that compromise traceability. Herein, two copper(I) iodide hybrid materials, denoted as 1D-Cu and 2D-Cu, are reported, which undergo an ethanol-triggered irreversible structural transformation from 1D-Cu to 2D-Cu. This transformation induces a pronounced photoluminescence redshift from weak green emission (539 nm, PLQY = 0.15%) to intense orange-red emission (639 nm, PLQY = 30.25%), accompanied by markedly enhanced thermal stability. Structural and spectroscopic analyses reveal that the superior stability and optical performance of 2D-Cu arise from strong intracluster Cu···Cu interactions (2.577-2.928 Å) and reinforced organic-inorganic interfacial interactions. Exploiting this irreversible transition, a dual-mode anticounterfeiting platform is developed. The visible-light mode enables self-erasable information display using phenolphthalein, while under UV excitation, the permanent fluorescence transformation serves as a visual and irreversible record of unauthorized access on paper substrates. This work demonstrates the potential of irreversible structural transitions in copper halide materials for high-security anticounterfeiting and traceability applications.