Mesogenic behaviour of p-nitrophenyl group linked with biphenyl mesogens via flexible spacers

摘要

Three series of nematogens with a terminal p-nitrophenyl group linked with biphenyl groups via flexible spacers were synthesised and their transitional properties were studied by means of differential scanning calorimetry (DSC) and polarising microscopy (POM). The nematic-isotropic transition temperature and the associated entropy change showed an odd-even effect as the length of the spacers was varied, in which the even members exhibited higher values. Such an odd-even effect was in consistency with the feature of liquid crystal dimers and trimers. On the basis of these data, it seemed reasonable to assume that the terminal p-nitrophenyl group played a role of mesogen in the nematic liquid crystal. The p-nitrophenyl group may work as a mesogen as a result of the interaction with the biphenyl mesogens. The mesogenic behaviour of the terminal p-nitrophenyl group is explained on the basis of neighbouring group effect.