Cellulose‐based films with ultralong full‐color circularly polarized room‐temperature phosphorescence and bidirectional dissymmetry tuning

Circularly polarized room‐temperature phosphorescence (CP‐RTP) materials with long lifetimes and large luminescence dissymmetry factors ( g lum ) are of great interest in chiral photonics, as g lum directly determines chiroptical performance for high‐end optoelectronic applications. In this work, we present a facile strategy to fabricate bio‐based CP‐RTP materials by embedding phosphorescent chromophores and polymers into the intrinsic chiral microenvironment of cellulose nanocrystal (CNC) films. Rigid crosslinked polymer networks suppress nonradiative exciton decay, giving the co‐assembled films an ultralong phosphorescence lifetime of 1.588 s, and guest dye doping further enables full‐color CP‐RTP emission via Förster resonance energy transfer. However, polymer incorporation disrupts the native chiral nematic ordering of CNC films, resulting in only moderate g lum values; in addition, the as‐prepared single‐layer films only produce unidirectional circularly polarized luminescence (CPL) due to the inherent left‐handed chiral structure of CNC assemblies. To overcome these limitations, we integrate an auxiliary CNC chiral filter with the CP‐RTP emissive layer to modulate chiral light propagation paths through selective Bragg reflection. This strategy enables simultaneous tuning of CPL sign and magnitude without sacrificing phosphorescence intensity, achieving g lum tuning across a range from −0.7782 to 0.2663. The resulting materials show good potential for a range of chiral photonic applications, especially optical security, as demonstrated by proof‐of‐concept encrypted patterns and anti‐counterfeiting labels.