Phase transitions in novel disulphide-bridged alkoxycyanobiphenyl dimers

The synthesis, characterization and mesomorphic properties of the first examples of novel disulphide- bridged alkoxycyanobiphenyl dimers are reported. The thermal behaviour of these mesogens was investigated by polarizing optical microscopy, differential scanning calorimetry and X- ray diffractometry. The dimers with a shorter spacer exhibit only the nematic phase while dimers with a longer spacer display nematic as well as smectic phases. X- ray diffraction experiments reveal the intercalated structure of the SmA phase of these dimers and the presence of short range SmA- like order in the N phase ( cybotactic nematic) of all the compounds, except the one with the shortest spacer.