Dual-Stimuli Chromogenic Membranes for Optical Security: Photochromic and Halochromic Anti-Counterfeiting...

A dual-stimuli chromogenic platform based on spiropyran-functionalized anodic aluminum oxide (SP-t-AAO) membranes with reversible photochromic and halochromic switching is reported. Surface characterization by electronic images confirms the well-preserved nanoporous morphology, while Energy-dispersive X-ray spectroscopy (EDS) scans reveal uniform grafting to micrometer depths. Grazing incidence X-ray photoelectron spectroscopy (GIXPS) and time-of-flight secondary ion mass Spectrometry (TOF-SIMS) further confirm successful surface chemical modification and pattern fidelity. Orthogonal functionalization is achieved via thiol-yne chemistry and spatially controlled photopatterning using Chinese seasonal-themed photomasks. Upon UV irradiation, the membrane exhibits a pale-to-magenta color change because of spiropyran-merocyanine isomerization; acid exposure further switches the color from magenta to yellow. Both transitions are fully reversible under white light or base treatment. Video analysis reveals rapid halochromic switching kinetics (0.4-4 s), highlighting excellent optical responsiveness. The membrane also demonstrates the chelation toward heavy metal ions such as Cu²⁺ and Fe²⁺. Moreover, thermal cycling test shows moderate durability, and a 20-day ambient test confirms excellent chromogenic stability. This work offers high-speed responsiveness, spatial precision, and long-term stability for anti-counterfeiting and sensing applications.