A New Class of Chiral Nematic Phase with Helical Polar Order

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Abstract
A novel chiral nematic phase with a polar helical order is realized via the introduction of helical twisting power into a polar nematogen. The properties of the induced polar nematic (polar cholesteric: Np*) phase differ from those of the conventional cholesteric (N*) phases existing thus far. Np*, which is a new class of N* structures, is characterized not only by its helically twisted nematic director, but also by a continuously twisted polarization. Transmission spectroscopy and helical pitch measurements in a wedge cell revealed that the half‐helical pitch in the Np* phase vanished because of the polar response in the Np* helix. The inner polar director in the Np* phase is confirmed in dielectric and second‐harmonic‐generation studies. Furthermore, this unique Np*LC, which corresponds to a half‐/full‐pitch helix, enables ultrafast electro‐optic switching (τ < 20 µs), and proposes new potential applications for electrically interchangeable photonic bandgaps.

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