ABSTRACT Chiral nematic liquid crystals are one‐dimensional photonic bandgap materials whose reflection wavelength can be tuned by temperature, but only limited and irreversible tuning can be achieved by electric fields. Oblique heliconical chiral nematic materials blueshift under electric fields applied along the helix axis, whereas chiral ferroelectric nematic ( liquid crystals can be redshifted by fields applied perpendicular to the helix axis. Here we demonstrate that in liquid crystals, the reflection color can be reversibly tuned by electric fields applied along the helix axis. In sandwich cells assembled with bare conducting indium tin oxide (ITO) substrates, the reflectivity peak wavelength increases by up to 200 nm under fields up to 0.4 V/µm. When the ITO substrates are treated with an electrically insulating polymer layer, the reflectivity shift is suppressed. We propose a theoretical model assuming helical deformation of the helix axis under an electric field. This model accounts for all experimental observations and yields an estimate of the splay elastic constant, which is challenging to determine by other methods. Our findings expand understanding of ferroelectric nematic liquid crystals and suggest potential applications in both tunable reflectors and energy‐efficient smart windows.
Himel et al. (Tue,) studied this question.