Circularly polarized luminescence is of paramount importance for applications in information encoding, bioimaging and optoelectronic devices. Cellulose nanocrystals derived from natural cellulose form aggregated nanorods in dispersions that self-assemble into a left-handed chiral nematic structure above a critical concentration and such an order can be preserved upon drying, producing freestanding transparent films with tunable photonic bandgaps and brilliant iridescence. The left-handed chiral nematic cellulose nanocrystal films feature intrinsic circular polarization ability, which enable selective reflection of left-handed circularly polarized light, selective transmission of right-handed circularly polarized light and right-handed circularly polarized luminescence due to the underlying one-dimensional photonic bandgaps.1,2 (Adv. Mater. 2018, 30, 1705948; Adv. Optical Mater. 2018, 1801246) The circular polarization ability of cellulose nanocrystals films has been extended to enable optically ambidextrous reflection and luminescence in a left-handed chiral nematic structure with intercalated nematic-like defect achieved by synergistic self-assembly and kinetic arrest.3 (CCS Chem. 2020, 2, 932–945) To date, the circular polarization ability of cellulose nanocrystals in the near-infrared II spectral regime, to the best of our knowledge, remains unexplored. Here we show that cellulose nanocrystals spontaneously form left-handed chiral nematic structures with the selective reflection bands in the spectral range of 1000-1700 nm. We demonstrate that such chiral nematic structures are capable of transforming spontaneous luminescence to photonic bandgap-based right-handed circularly polarized luminescence with the dissymmetry factors up to -0.33 in the near-infrared II spectral regime. Photonic bandedge-stimulated circularly polarized luminescence occurs. The chiral environment effect on the luminescence dissymmetry factor is observed. We showcase how the near-infrared II circularly polarized luminescence can be utilized as a probe for cancer diagnose applications. Our work extends the intrinsic circular polarization ability of cellulose nanocrystals and presents new opportunities for the biosourced chiral nematic materials in biomedical applications.

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