Terminal branches, swallow-tailed mesogens

Swallow-tailed mesogens are characterized by a bulky alkyl branch connected to a terminal ring by a functional group or spacer. Thus such mesogens contain at one terminal end two long chains, and the molecular shape is therefore wedge-like and should be considered as a steric dipole. Most exam-... 

Table 13. Further chemical structures of terminal branches of swallow-tailed mesogens.

In principle, the terminal branches of swallow-tailed compounds can be attached at both ends of a rod. However, only dialkyl benzylidenemalonates have been used extensively to prepare double-swallow-tailed mesogens. The minimum size of the basic mesogen is four cyclic units, these mostly being phenyl rings [85]. The clearing points in the series 45 decrease strongly with in-... 

Even if they are not, strictly speaking, polycatenar molecules, double swallow-tailed compounds with long branches can be considered as a special case of tetracatenar mesogens, where the branches are not directly attached to the terminal rings [57], as shown in Fig. 10. 

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