Optical activity and linear electrooptic response in the paraelectric subphase of an achiral ferroelectric nematic compound

Polarizing optical microscopy and electro optics are used to study a compound with constituent non-chiral molecules, DIO, known to exhibit three nematic phases, namely N, Nx and ferronematic N_F. N is found to be a conventional nematic but shows two additional unusual features: the presence of optically active domains and a linear electro optic response to the applied signal. The optical activity is explained by a segregation of the stable helical conformers of the opposite sense; these preferring to form domains with an optical rotation of ±4°/μm. This is the first example of helical segregation observed in non-chiral molecules in the high temperature nematic phase. Unlike the ordinary nematic liquid crystalline material, this compound shows a linear electro optical response to the applied electric field, thereby confirming the polar nature of this phase. N_F is the ferroelectric nematic as reported previously. The strong polar azimuthal surface interaction energy in the N_F phase stabilises a homogeneous structure in planar-aligned cells that are rubbed parallel and gives a twisted structure in cells rubbed antiparallel.