Design, synthesis and mesomorphic behaviour of a four-ring achiral bent-core liquid crystal in the nematic phase

Abstract

Bent-core nematics have attracted growing interest because of the unconventional properties and extraordinary effects exhibited by these liquid crystalline phases. In this report we design, synthesize and characterize four different four-ring achiral bent-core liquid crystals containing a methyl group in the central phenyl ring. The mesomorphic behaviour of compounds has been investigated by optical polarizing microscopy, differential scanning calorimetry, electro-optical investigation, and dielectric spectroscopy. Calculations based on density functional theory of the molecules were also carried out. The addition of a methyl group in the central phenyl ring not only induces the lowering of the clearing point but also enhances the nematic phase range. Dielectric spectroscopy reveals a low frequency relaxation peak and a very large dielectric permittivity; which is the characteristic of cybotactic clusters. In electro-optic studies, spontaneous polarization peaks are not observed. However, a periodic pattern is observed under the application of an ac electric field. Finally, the compounds show a weak tendency to crystallize; which makes it possible to supercool the cybotactic nematic phase down to room temperature.