The Structure and Unusual Optical Textures of Smectic C2 Phases of New Tail-to-Tail Twins

New tail-to-tail twins with alkyl or perfluorinated spacers were synthesized. The mesomorphic properties were studied by polarizing microscopy and X-ray diffraction measurements. It was found that the smectic C phase is a Sc₂ phase with alternating tilt and an intercalated structure. The alternating tilt gives rise to an unusual schlieren texture which exhibits not only singularities with the strength s = ±1 but also those with s = ±1/2 and s = ±3/2.