Elastic and electro-optical properties of flexible fluorinated dimers with negative dielectric anisotropy

We report the synthesis and temperature dependencies of optical, dielectric, elastic properties four homologous dimeric mesogens in uniaxial nematic (N) phase. The studied dimers are derived from 2ʹ,3ʹ-difluoroterphenyl units connected via flexible alkyl chains. compounds differ length either chain or terminal groups. These achiral bimesogens exhibit twist-bend (NTB) phase with a nanoscale pitch modulated director, as established by freeze-fracture transmission electron microscopy. All homologs have negative dielectric anisotropy owing to permanent dipole oriented normal long molecular axes. A longer bridge yields an expanded range N phase, stronger anisotropy, larger birefringence bend constant K33. Longer chains increase but decrease absolute value show dramatic K33 down ~0.5 pN on approaching N-NTB transition. period modulation NTB