Thermotropic Biaxial Nematic Liquid Crystals

We have synthesized liquid crystal (LC) mesogens based on a nonlinear oxadiazole unit that exhibit nematic phases near $200°\mathrm{C}$. Polarized microscopy and conoscopy indicate that these LCs are biaxial nematics. Unambiguous and quantitative evidence for biaxiality is achieved using ${}^2\mathrm{H}$ NMR spectroscopy. “2D powder” spectra, obtained by rotating ${}^2\mathrm{H}$-labeled samples about an axis perpendicular to the magnetic field at $\sim 200\mathrm{Hz}$, yield phase biaxiality parameters of $\sim 0.1$ when coupled with rigorous and proven simulations.