Water-triggered stimuli-responsive luminescent crown-ether-coordinated cuprous bromides for multi-functional applications

Stimuli-responsive photoluminescent materials have garnered considerable attention due to their immense potential in enhancing security protection. However, achieving high-level multimodal anti-counterfeiting remains a challenge. In this work, we report on water-triggered stimuli-responsive luminescent crown-ether coordinated cuprous bromides (CCB) for multi-functional applications. The CCB powders were synthesized via mechano-chemical grinding CuBr, NaBr and 18-crown-6 ether (18C6) together. Depending on the amount of 18C6 incorporated into the reaction, the blue and green emission composites were obtained, respectively. Upon contact to water and subsequent thermal dehydration, both powders exhibit a fascinating cyclic and reversible transformation in their emission hues, seamlessly alternating between blue/green and orange. The three distinct emission states were identified and characterized as (18C6)NaCuBr₂, (18C6)₂Na(H₂O)₂CuBr₂, and (18C6)₂Na₂(H₂O)₃Cu₄Br₆, respectively. These unique luminescent properties, coupled with their swift and repeatable stimuli-responsive behavior, position CCBs as novel and highly promising functional materials for applications in dynamic information storage and encryption. Based on CCBs, multi-modal anti-counterfeiting patterns and rewritable luminescent paper were successfully fabricated. Additionally, crown ether species and alkali metal ions exert a remarkable influence on the photophysical properties of CCBs. This research provides a novel strategy to develop multi-modal anticounterfeiting applications, expanding the horizons of security and authentication technologies.