Towards Room Temperature Biaxial Nematics

Abstract

A series of new liquid crystalline compounds based on the 2,5-bis-(p-hydroxyphenyl)-1,3,4-oxadiazole (ODBP) core was synthesized in an effort to access the biaxial nematic phase at low temperatures. Derivatives with secondary terminal alkoxy groups and derivatives with either two or four lateral methyl groups were prepared. Secondary alkoxy terminal groups either suppressed mesophase formation altogether or increased the nematic onset temperature relative to primary groups. The dimethylated derivatives showed significant reductions in the nematic onset temperatures compared to the previously reported unmethylated compounds. The tetramethylated analogs generally possessed low clearing temperatures, but exhibited only monotropic mesomorphism.

Keywords:

• biaxial nematic phase
• lateral methylation
• oxadiazole containing liquid crystals

Acknowledgments

We thank Drs. Dingemans, Madsen, and Zafiropoulos for helpful conversations. This work was supported by NSF grant DMR-9971143. Eric Scharrer also wishes to acknowledge the University of Puget Sound for a Lantz Sabbatical Award that allowed him to spend the 2006–07 academic year at the University of North Carolina.

Notes

^a All temperatures and enthalpies are based on the second DSC heating run.

^b This represents an uncharacterized smectic phase.

^c Temperatures in brackets indicate a monotropic transition.