Time-Resolved Photochromic Ionic Hydrogen-Bonded Organic Frameworks for Multimodal Advanced Information Protection

Stimuli-responsive luminescent materials have strong attraction in the field of information anticounterfeiting encryption due to their unique response characteristics. Introducing a time-resolved strategy can expand the encryption dimension from static localized variables to dynamic spatial stereoscopic evolution, achieving high-order security beyond traditional static encryption. This study is based on bis(benzene-p-sulfonic acid)-naphthalenediimide (p-H₂BSNDI) and (1R/S,2R/S)-1,2-diphenylethylenediamine (R/S-DPEN) and successfully constructs R/S-iHOF-67 with excellent photochromic properties through charge-assisted supramolecular self-assembly to achieve time-resolved information encryption. The iHOF-67 solid powder can change from pale yellow to light brown in 1 s, exhibiting high-contrast photochromic photophysical properties. To realize the multimodal encryption requirements, iHOF-67 can be dispersed in poly(vinyl alcohol) (PVA) matrix or organic solvents to inhibit aggregation-caused quenching (ACQ) interactions and enhance its fluorescence intensity. Interestingly, under UV excitation, the 0.5%-iHOF-67@PVA membrane exhibits excellent photochromic properties and time-resolved dynamic fluorescence behavior. This behavior is achieved through the Förster resonance energy transfer (FRET) process. Therefore, a dynamic color-changing QR code based on 0.5%-iHOF-67@PVA realizes advanced encryption and anticounterfeiting of information in the time dimension. In addition, the fluorescence of iHOF-67 also changed with the polarity of the solvents. Based on this characteristic, this work developed a multicolor fluorescent ink solution. It is combined with the spatial encoding strategy of a 3D Rubik's Cube to construct a 4D information encryption system with temporal resolution. This strategy significantly increases anticounterfeiting complexity and decryption difficulty, thus providing references for designing wide-range, time-resolved, multimodal information protection technologies.