Dynamically photoregulated multicolor materials for accurate color-difference-based information encryption

In this study, a multicolor luminescent material (TSS) was prepared by lanthanide ions (Tb 3+ ) with 2-hydroxybenzoic acid (SA) and spiropyran (SP). TSS exhibited dynamically tunable dual-mode color (optical and fluorescent colors). The absorption and fluorescence spectra revealed that the changes in dual-mode color of TSS depended on the duration of the visible (Vis) irradiation time (t) and excitation wavelength (λ). Consequently, the optical color of TSS can be modulated from orange to colorless with varying t, while its fluorescent color changed from red to green and blue to cyan under 365- and 254-nm ultraviolet (UV) lamp, respectively. The combined effects of fluorescence resonance energy transfer (FRET) between SP and Tb 3+ and the inner filter effect (IFE) between SP and SA contributed to the rich multicolor of TSS. Moreover, the cascade effect of FRET and IFE imparted TSS with fine and tunable time-related features. By employing the color difference value (ΔE) to measure the changes in the dual-mode color of TSS, a binary output logic gate based on ΔE was proposed to realize accurate information encryption and decryption. Furthermore, the ΔE-based encryption strategy enhances the information encryption capacity of multicolor materials through the subdivision of ΔE. This approach provides a cost-effective means of achieving high-capacity information output. Thus, the ΔE-based encryption strategy significantly improves the efficiency of multicolor material utilization. This study demonstrates significant potential for further accurate and low-cost encryption.