PHYSICAL JOURNAL E

Abstract. We present a polarising optical microscopy study of the low-temperature anticlinic-like tilted mesophase of the liquid-crystal compound octylphenyl-2-chloro-4-(p-cyano-benzoyloxy) (DB8Cl). This mesophase has been described as a bilayer smectic structure in which the molecules within each layer are organised in an anticlinic way. The optical textures observed in samples with planar orientation show a double stripe pattern, with the lines aligned parallel to the rubbing direction, characteristic of a double periodic modulation of the refractive index of the material. The long-period modulation is temperature de-pendent and disappears for thin sample cells (< 5m). The short-period modulation is nearly independent of the thickness of the cells. The experimental results are analysed in terms of a model which considers that there is a special distribution of the principal optical axis which may be in or out of the polariser-analyser plane. The observed periodic variation of the principal optical axis could not be interpreted in terms of the original structure proposed for this phase. DB8Cl presents a structure formed by dimers that can be viewed as °exible bent-core{like molecules, showing similarities with phases found in banana-like systems, but exhibiting a much more complex structure. PACS. 61.30.-v Liquid crystals { 61.30.Eb Experimental determinations of smectic, nematic, cholesteric, and other structures { 77.84.Nh Liquids, emulsions, and suspensions; liquid crystals