Triple-modal secure films with non-contact color modulation for spatiotemporal encryption pixels

Dynamic optical materials show significant potential for advanced information encryption and anti-counterfeiting, yet multimodal non-contact decryption systems remain challenging. Herein, a feasible strategy is proposed for spatiotemporal encryption through non-contact modulation of structural color (SC), photochromic color (PC), and fluorescent color (FC). This secure film is achieved via compartmentalized microdroplet encapsulation and curing (CMEC) technique based on crosslinked polydimethylsiloxane. The microdroplet integrates three components: (i) superparamagnetic Fe 3 O 4 @SiO 2 nanoparticles (SPIONs) for magnetically responsive SC modulation, (ii) methyl-functionalized spiropyran (MSP) for reversible PC switching and (iii) nitrogen-doped carbon dots (NCDs) that enable time-evolving FC transitions via fluorescence resonance energy transfer with MSP. Initial static information concealment is achieved via optimization of SPIONs parameters. Spatial encryption synergizes SC (red to purple) with PC (red), while temporal security stems from adjustable FC (from blue through pink to red). The CMEC strategy allows facile preparation of multimodal films with versatile compositions. We arrange pixel arrays in single, dual, and triple modes. This yields a Morse-code-based spatiotemporal encryption system that affords over 7.9 × 10 28 rewritable programming possibilities. This methodology establishes a generalizable platform for multimodal high-security encryption systems toward practical applications.