Engineering pitch gradients via thermal processing of enantiomeric glassy liquid crystals

Abstract

The selective reflection and circular polarization characteristics of cholesteric liquid crystals (CLCs) arise from their self-assembly into helicoidal structures, producing photonic stopbands typically 50–100 nm wide. Here, we demonstrate that thermal annealing of enantiomeric cholesteric glassy liquid crystals (ChGLCs)—differing only in stereochemistry—can generate pitch profiles that broaden the photonic stopband across the full visible spectrum. The resulting structures are permanently fixed by vitrification into the glassy state. When adjacent ChGLC layers share the same handedness, enantiomer diffusion follows Fickian-like behavior, enabling predictable gradient formation. In contrast, when layers of opposite handedness are annealed, molecular diffusion is strongly suppressed, and no stopband broadening is observed. These results clarify how chirality influences molecular mobility in chiral liquid crystalline media and establish a robust approach for engineering broadband optical films with tunable reflection properties. This strategy provides a platform for designing next-generation photonic materials, including broadband reflectors, polarization optics, and reconfigurable coatings.