Intrinsically chiral ferronematic liquid crystals: An inversion of the helical twist sense at the chiral nematic – Chiral ferronematic phase transition

Abstract

The ferroelectric nematic phase is a unique example of a polar phase without positional order of the constituent molecules. The properties of the ferronematic phase formed by intrinsically chiral molecules are discussed. Chirality makes the phase structure helical with the similar pitch length in the N* and N F * phases, but with opposite sense. The materials show strong non-linear optical properties. • Intrinsically chiral mesogens forming ferroelectric fluidic nematic, N F *, phase were obtained and studied. • In both, paraelectric and ferroelectric nematic phases, molecular chirality leads to helical structure. • Inversion of helix twist sense was observed at the N*-N F *phase transition. • Giant dielectric permittivity, above 10 4 , was determined in ferroelectric nematic phase. • Strong nonlinear optical properties were confirmed for ferronematic phase. Strongly dipolar mesogenic compounds with a chiral center located in a lateral alkyl chain were synthesized, and shown to form the ferroelectric nematic phase. The presence of molecular chirality induced a helical structure in both the N* and N F * phases, but with opposite helix sense in the two phases. The relaxation frequency of the polar fluctuations is only weakly affected by helical structure, it was found to be slightly lower for the chiral N F * phase than for its achiral, non-branched counterpart with the same lateral chain length.