Redox‐Modulated Circularly Polarized Luminescence in Chiral Photonic Films Derived from Cellulose Nanocrystals and Polyoxometalate

Achieving smart circularly polarized luminescence (CPL) materials with large luminescence dissymmetry factor ( g lum ) is in high demand for potential technological applications in the chiroptical fields. Herein, a series of chiral photonic crystals (CPCs) derived from cellulose nanocrystals (CNCs) and photosensitive inorganic polyoxometalates (POMs) through an evaporation‐induced self‐assembly strategy are reported. The photonic bandgaps (PBGs) of CPC films are well regulated by controlling the amount of doped POMs, yielding the tunable right‐handed CPL emission with tailored g lum . By locating the maximum emission peak of POMs at the center of the PBG of CPC films, the composite shows remarkable CPL performance with a | g lum | value up to 0.53. Furthermore, the CPL can be reversibly switched on/off through a fluorescence resonance energy transfer (FRET) process controlled by alternate UV irradiation reduction and air oxidation. The CPC films hold the great promise as next‐generation chiroptical memory devices.