Photonic Bandgap in Achiral Liquid Crystals—A Twist on a Twist

Achiral mesogenic molecules are shown to be able spontaneously assemble into liquid crystalline smectic phases having either simple or double-helical structures. At the transition between these phases, structure unwinds. As a consequence, in some temperature range, pitch of helix becomes comparable wavelength visible light and selective reflection range is observed. The photonic bandgap phenomenon reported for achiral crystals.