The effect of molecular structure on the chiral random grain boundary phase

Abstract

ABSTRACTA chiral random grain boundary (RGB) phase was recently observed in a hockey-stick biphenyl-substituted 1,3,4-oxadiazole derivative. In the RGB phase, achiral molecules self-assemble into randomly oriented blocks of chiral smectic layers and the motif of the unique microstructure is attributed to the similarity of hockey-stick molecules both to bent-core and to rod-like molecules. In order to explore the effect of molecular structure on the RGB phase in detail, we systematically change the molecular design. When the flexible tail decreases, the high-temperature Smectic A (SmA) phase is replaced by a nematic phase, showing a phase sequence of Iso-N-SmA-RGB-Cryst in 2-(4-dodecyloxyphenyl)-5-biphenyl-1,3,4-oxadiazole. However, when we replace the 1,3,4-oxadiazole group by the 1,3,4-thiadiazole group, the bending angle increases in the 1,3,4-thiadiazole derivatives and the RGB phase disappears. Or when the length of the arm becomes short in naphthalene-substituted 1,3,4-oxadiazole, these molecules exhibited only normal rod-like molecules’ mesomorphism. These results will provide deep insights on the relationship of molecular structure and mesophase structural property.