Pressure‐Induced Inversion of Chiroptical Properties in Cholesteric Assembled Cellulose Nanocrystals

Abstract

Dynamic manipulation of the chiroptical effect, particularly the inversion of chiral signal, has attracted broad attention, but still remains challenging, Here, stepwise tuning of the helicoidal assembly and chiroptical properties of the cellulose nanocrystal (CNC) films utilizing high pressure are demonstrated. With in situ monitoring, the changes of Fourier‐transform infrared (FTIR) spectra and evaluating the corresponding applied energy, three distinctive stages of chiroptical properties are clearly identified. In these stages, the photonic bandgap of the CNC film exhibits a fast‐slow–fast alteration over different energy imposed. The three stages are associated sequentially with interlayer space reduction, hydrogen bonding reconfiguration, and covalent bands changing. A switch of chiral signal from left‐ to right‐handedness is observed in the third stage, and the handedness of CD spectra can be recovered upon release, which is barely observed. This unique property is suspected to be the change in CNCs assembly induced by molecular‐level conformational change. This work sheds light on the fundamental understanding of how pressure can trigger the change from molecular‐level to hierarchical assembly and corresponding chiroptical performance, facilitating the design of chiral assembly with pre‐programmed triggering chiroptical properties of bio‐photonic materials.