Chiral nematic liquid crystals prepared with Grandjean texture demonstrate a photonic bandgap whose central wavelength is proportional to the pitch length, P, of the liquid crystal and whose width is given by (ne – no)P. We show that methyl red doped chiral nematics undergo a shift in the photonic bandgap upon photo-isomerization. This shift is a result of (1) photo-induced change in anchoring energy on the nematic surface, and (2) change in the natural pitch length from the photo-isomerization of the azo dye.
Hysteresis and Fréedericksz thresholds for twisted states in chiral nematic liquid crystals: Minimum-energy path approach