Next‐generation photochromic smart window: Wood‐derived cellulose flexible composites integrated thermal insulation, UV‐shielding, and anti‐counterfeiting

Abstract Addressing the dual challenges of global energy sustainability and dynamic optical management, we present an innovative flexible photochromic transparent fluorescent wood composite film (PT‐FWF) with molecular‐scale engineered design, fabricated through in situ Eu 3+ coordination on TEMPO‐oxidized cellulose scaffolds. This hierarchically structured material combines fluorescent wood film with hot‐pressing, impregnation, and coating (PMMA/WO 3 ) to achieve multimodal optical control. PT‐FWF demonstrates exceptional multifunctionality: 88% optical transparency, 107.5° ± 1.0° hydrophobicity surface, and thermal insulation (Δ T ≈ 5.5°C). A unique dual‐mode photoresponsive mechanism enables through synergistic photochromic‐fluorescent effects: instantaneous fluorescence under UV light and coloring/bleaching with or without light‐assisted (UV or simulated sunlight). The smart window model exhibits over 90% UV‐blocking efficiency, and the transmittance of the smart window can be reversibly switched between 88% and 5% under prolonged light conditions, showing a high modulation of visible light (∆ T lum = 83%) at 1030 nm, enabling simultaneous daylight optimization and energy conservation. This molecular‐scale engineered wood composite defines a transformative platform for adaptive optical materials, merging energy‐efficient architectural solutions with information encryption through sunlight‐regulated smart windows that simultaneously enable environmental protection and anti‐counterfeiting. image