The biaxial nematic phase of oxadiazole biphenol mesogens

Abstract

Herein we review the attributes of the cluster biaxial nematic exhibited by bent-core mesogens derived from the oxadiazole biphenol mesogenic core. We present an array of static ²H NMR spectra as well as 2D powder spectra generated by rotating the nematic phase of directly labelled mesogens. Analysis of these motionally averaged NMR observations requires the nematic phase to have monoclinic symmetry. X-ray diffraction data, in particular the effects of electric and magnetic field effects, are also consonant with the cluster picture of this biaxial nematic phase.

Keywords:

• liquid crystal
• nematic
• biaxial
• cybotaxis
• bent-core
• mesogen

Acknowledgements

The authors acknowledge C. Ferrero F. Fauth, J. Gorini, E. Di Cola and T. Narayanan (ESRF) for their technical support in XRD measurements. We are grateful to Dr Perttu Lantto (University of Oulu) for computing the chemical shift anisotropies of the aromatic deterons. ETS thanks the Boshamer Professorship Endowment for support.

Notes

1. 1. Earlier interpretations of XRD as evidence for biaxiality (an absence of cybotaxis and E-field-induced changes in diffraction [9] have been called into question and subsequent X-ray studies on this class of ODBP liquid crystals suggest that cybotactic clusters in fact give rise to the unique experimental observations, namely the ‘four-spot’ low-angle diffraction pattern, and thermodynamic phase changes account for the influence of an external E-field on diffraction pattern [10,11].

2. 2. The CSA of aromatic deuterons were calculated by Dr. Perttu Lantto using DFT.