Photoswitchable Pseudorotaxanes with Dual Chromism and Tunable Fluorescence for Multilevel Information Encryption

The design and construction of mechanically interlocked molecules (MIMs) displaying distinct physical/chemical properties under different states is highly desirable due to their multifunctional applications. Herein, we report a photoswitchable pseudorotaxane system constructed through host - guest interactions between a vinyl-bipyridinium axle and cucurbit[7]uril (Q[7]) macrocycle. Upon light irradiation, the [3]pseudorotaxane E-G²⁺@Q[7]₂ in aqueous solution undergoes E→Z photoisomerization, converting to the [2]pseudorotaxane Z-G²⁺@Q[7], where Q[7] selectively encircles the central Z-vinyl-bipyridinium unit. Notably, E-G²⁺@Q[7]₂ displays dual photochromic and vapochromic (NH₃) activity, whereas Z-G²⁺@Q[7] is optically and vapor-responsively inert. Additionally, both E-G²⁺@Q[7]₂ and Z-G²⁺@Q[7] exhibit distinct solid-state fluorescence emissions due to macrocyclic confinement effects. By leveraging these stimuli-responsive properties, we developed a multilevel information encryption system with three decryption states controlled by wavelength-specific irradiation (365 nm, 430 nm, or xenon lamp), enabling programmable message display via fluorescence and color changes. This work provides a paradigm for designing smart materials with integrated photoswitching, chromic, and fluorescent functionalities for advanced security applications.