Mechanically robust cellulose nanocrystal photonic films with propagation-switchable circularly polarized room-temperature phosphorescence

. Notably, the asymmetric PVA/CNC architecture enables enantiomeric switching of CPL handedness through a propagation-direction-dependent reflection-transmission mechanism. Under top-side excitation, the selective reflection of L-CPL allows the detection of transmitted R-CPL, whereas bottom-side excitation leads to the detection of L-CPL, enabling dynamic chiroptical modulation and multilevel optical encryption. This work provides a feasible strategy for mechanically robust CPRTP photonic materials for advanced optical encoding and information security applications.