Synthesis of liquid crystals bearing 1,3-dioxane structures and characterization of their ferroelectricity in the nematic phase

Abstract

Various structured C3-DIO analogues were synthesized, and their structural and physical properties in liquid crystal phases were investigated through differential scanning calorimetry, polarization optical microscopy, dielectric relaxation, and polarization current measurements. The replacement of fluorine atoms and substitution of other polar functional groups in the C3-DIO structures significantly affected their phase transition behaviour and the emergence of the ferroelectric nematic phase. Among the analogues of C3-DIO, the dipole moments and the generation of the ferroelectric nematic phase were found to be correlated; analogs with vector-added dipole moments below 8.5 D over the whole molecular structure show only the paraelectric nematic phase, whereas those with vector-added dipole moments above 8.5 D over the whole molecular structure show the ferroelectric nematic phase. In particular, the analogue bearing a cyano group gives a large dipole moment of more than 13 D and gives rise to a dielectric constant of more than 14 000 at 100 Hz in its ferroelectric nematic state. The introduction of electron-withdrawing groups at the 4-position of the benzene ring furthest from the dioxane unit in C3-DIO is effective for the enhancement of whole dipole moments and generation of the ferroelectric nematic phase. Our results provide valuable insights into the design of DIO-based molecules with ferroelectric nematic phases.