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  c hiral 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 arrangement  of fine size .  Three levels of chirality  exist in the  CMBFs:  primary  twisting 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 results of enhanced resonance due to structural handedness matching and synergic effect of multi-OAs.