The Layer Structure in Smectic A Phases and the Phase Transition Behavior for Cyano- and Nitrofuran Compounds

The layer structure and phasetransition behavior of smectic A phases for 4-(4-alkoxyphenoxycarbonyl)phenyl 5-X-furan-2-carboxylates (X = CN, NO2) were examined by a small-angle X-ray diffraction method. The higher homologs of both compounds exhibit two kinds of smectic A (Sm A) phases and experience the Sm A-Sm A transition. One Sm A phase exhibited at a higher temperature region having a layer spacing of 1.5-1.9 times the calculated molecular length; and the layer spacing gradually increases with decreasing temperature. The other Sm A phase exhibited at a lower temperature region having a layer spacing of twice the calculated molecular length; also, the layer spacing is almost independent of the temperature. The Sm A-Sm A transition behavior is discussed.