Asymmetric oxadiazole mesogens as candidates for low-temperature biaxial nematics

Abstract

We report the synthesis and properties of a homologous series of asymmetric, mesogenic derivatives of 2,5-bis-(p-hydroxyphenyl)-1,3,4-oxadiazole (ODBP). Benzyloxy (BnO-), alkoxy benzoate ester derivatives BnO-ODBP-Ph-O-C _n , where n = 4, 5, 6, 7, 8, 9, 12, were studied by ²H-NMR, X-ray diffraction and polarising microscopy in order to ascertain if the lower temperature nematic phases exhibited biaxiality. Deuterium nuclear magnetic resonance (NMR) of labelled probes in these asymmetric mesogens does not show evidence of biaxiality. The absence of biaxiality is discussed in terms of the statistical non-linearity of these asymmetric ODBP mesogens.

Keywords:

• biaxial nematics
• oxadiazole derivatives
• structure-property relationship

Acknowledgements

We thank Dr. Louis Madsen for advice with the NMR spectroscopy. This work was supported by NSF grant DMR-9971143 and DMR-0605923.