An optically uniaxial antiferroelectric smectic phase in asymmetrical bent-core compounds containing a 3-aminophenol central unit

Abstract

Two new series of asymmetrical bent-core compounds possessing 3-aminophenol and its N-methyl derivative were synthesized. In the obtained compounds, the asymmetry comes from the different linkages between the central unit and its arms and in two cases also from different lateral substituents. The mesomorphic properties were investigated by differential scanning calorimetry, polarizing optical microscopy, switching current and electro-optical measurements, X-ray analysis, and second-harmonic generation. All materials possessing 3-aminophenol as a central unit showed liquid crystalline properties, and two of them exhibited the orthogonal smectic phase (SmA family phase) and very stable columnar phases, while the N-methyl analogues exhibited no mesophase. Because of the optically uniaxial nature, double switching current peaks, and SHG activity associated with a distinct threshold electric field, this orthogonal smectic phase is assigned to a novel type, which has a short-range antiferroelectric order with a long-range randomized polar plane (SmAP_AR). This is very unique in the sense that distinct threshold behavior emerges at the field-induced phase transition from the short-range antiferroelectric phase to a long-range ferroelectric phase.