The biaxial nematic liquid crystalline phase was predicted several decades ago. Several vigorous attempts to ???nd it in various systems resulted in mis-identi???cations. The results of X-ray diffraction and optical texture studies of the phases exhibited by rigid bent-core molecules derived from 2,5-bis-(e?‘?-hydroxyphenyl)-1,3,4-oxadiazole reveal that the biaxial nematic phase is formed by three compounds of this type. X-ray diffraction studies reveal that the nematic phase of these compounds has the achiral symmetry D2h, in which the overall long axes of the molecules are oriented parallel to each other to de???ne the major axis of the biaxial phase. The apex of the bent-cores de???nes the minor axis of this phase along which the planes containing the bent-cores of neighboring molecules are oriented parallel to each other.
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