The 3rd International Symposium on Nanocellulosic Materials (3rd ISNCM)

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.