Synthesis of four-ring unsymmetrical bent-core mesogens and cybotactic cluster formation in their nematic phase

Abstract

The synthesis and characterization of novel achiral unsymmetrical four-ring bent-core molecules resembling a hockey-stick shape are described. The present compounds bearing a methyl substituent in the central phenyl ring exhibit the skewed cybotactic nematic (NcybC), smectic C (SmC) and additional tilted smectic phase with tilted molecular arrangement. The skewed cybotactic nematic phase is formed by the bent-core molecules with long range orientational ordered clusters possessing local smectic C type order and within a cluster of tilted molecular assembly. The previously reported four-ring compounds without the methyl moiety did not exhibit nematic phase but show polarization modulated B1revtilt phase. The x-ray diffraction pattern clearly indicated the existence of SmC-type cybotactic clusters over a wide N temperature range; the layer reflection peak is weak at a higher temperature region and becomes more conspicuous with decreasing temperature. The lower temperature phase is distinctly the SmC phase, and in addition another tilted smectic phase emerges below SmC.