Chiral Mesostructured BiOBr Films with Circularly Polarized Colour Response

Achieving strong and broadband circularly polarized colour responses in chiral inorganic materials is challenging. Here, we fabricated chiral mesostructured bismuth oxybromide (BiOBr) films (CMBFs) via hydrothermal growth using chiral sugar alcohols as symmetry-breaking agents. The layered slabs of BiOBr crystals with weak van-der-Waals interactions are prone to mismatching due to the chiral driving force, resulting in hierarchically chiral arrangements of fine size. Three levels of chirality exist in the CMBFs: primary, helical distortion crystal lattices of a nanoflake, secondary, helical stacking of nanoflakes to form nanoplates, and tertiary, chiral vortexes arranged by nanoplates. The CMBFs displayed optical activities (OAs) over a wide wavelength range of 350-2500 nm with an anisotropic factor of up to 0.99, which led to a significant chirality-dependent colour response to circularly polarized light. The high selectivity can be considered as the result of enhanced resonance due to structural-handedness matching and the synergistic effect of multiple OAs.