Solvent-engineered time-dependent hydrochromic perovskite nanocrystals in wool keratin for multi-level encryption with distinguishable temporal keys

To address the limitations of traditional time-dependent encryption materials, including complex synthesis, short fluorescence lifetimes (<1 s), high costs, and poor decryption distinguishability, this study develops a one-step solvent-engineering method based on a wool keratin (WK) matrix to fabricate time-dependent hydrochromic perovskite nanocrystals (PNCs). The inherent water solubility and abundant functional groups of WK simplify the synthesis process while eliminating the need for small-molecule ligands. By adjusting the solvent composition (H₂O, EtOH-H₂O, or DMF-H₂O) and their ratios, we achieve, for the first time, precise control over the hydrochromic response time of PNCs, ranging from seconds to minutes and days. The underlying mechanism involves solvent-evaporation-driven morphological evolution and enhanced β-sheet content in WK, which synergistically improve PNCs spatial confinement and encapsulation stability. This material platform enables time-dependent multi-level dynamic information encryption via “temporal keys”: PNCs@WK (EtOH 50 %, 3 s) < PNCs@WK (H₂O, 30 s) < PNCs@WK (DMF 50 %, >30 min). The multi-level dynamic information encryption exhibits robust cyclic stability, maintaining functionality over 20 cycles. This temporal distinguishability significantly enhances encryption security and resolution. Moreover, this WK-based solvent-engineering strategy demonstrates universal applicability to diverse PNCs configurations, offering a low-cost, sustainable solution for distinguishable time-dependent multi-level information encryption and decryption applications.