Photo‐Stimuli‐Responsive Dual‐Emitting Luminescence of a Spiropyran‐Encapsulating Metal–Organic Framework for Dynamic Information Encryption

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The development of photo-stimuli-responsive luminescent materials is essential to address emerging demands in encryption security. Here, a novel photo-stimuli-responsive dual-emitting luminescent material ZJU-128⊃SP (SP = spiropyran) is reported, which is obtained by encapsulating spiropyran molecules into a cadmium-based metal-organic framework (MOF), [Cd₃ (TCPP)₂ ]·4DMF·4H₂ O (ZJU-128, H₄ TCPP = 2,3,5,6-tetrakis (4-carboxyphenyl)pyrazine). This MOF/dye composite ZJU-128⊃SP exhibits a blue emission from the ligand of ZJU-128 at 447 nm and a red emission around 650 nm from spiropyran. Utilizing the photoisomerization of spiropyran from ring-closed to ring-open form under UV-light irradiation, significant fluorescence resonance energy transfer (FRET) process between ZJU-128 and spiropyran is achieved. As a result, the blue emission of ZJU-128 is gradually decreased while the red emission of spiropyran increases. This dynamic fluorescent behavior can fully recover to the original state following exposure to visible light (>405 nm). By taking advantage of the time-dependent fluorescence, dynamical anti-counterfeiting patterns and multiplexed coding are successfully developed based on ZJU-128⊃SP film. This work provides an inspiring point for the design of information encryption materials with higher security requirements.