General phase-structure relationship in polar rod-shaped liquid crystals: Importance of shape anisotropy and dipolar strength

Ferroelectricity is a property with spontaneous polarization, which is of paramount importance in modern electrooptic applications. Yet, its observations are mostly limited to solids or chiral smectic C liquid crystals with nearly no fluidity. The fluidic ferroelectrics, called ferroelectric nematics, have recently become available by incorporating strong polarity into the apolar liquid crystalline orientational field. Here, we present a rational principle for designing the ferroelectric materials and controlling their phase behaviors. We reveal that, while the apolar nematic order with the second-rank tensor originates from the shape anisotropy in the apolar nematic state, the polarization field serves as an additional mechanism for stabilizing polar nematic orders. Based on a comprehensive set of examinations and machine-learningdriven analyses for about 150 chemically distinct polar rod-shaped molecules, we uncover that the interplay between the shape anisotropy and polarization field gives rise to a diversification of the polar liquid crystal behaviors. The strategy offers much broader design flexibility and may facilitate the development of future polar functional liquid crystals.