Laterally dibenzyloxy-branched nematogens with large nematic range and rich solid polymorphism

Mesogenic compounds containing four rings in the core usually have very hig h melting points. However, when two identical lateral benzyloxy groups are introduced on the same side of one of the central rings, the melting point is lowered dramatically and a large nematic range is retained. This range i s affected by the bulkiness of the pam-substituents in the lateral rings. M ethyl groups can be introduced in the ortho- or meta-positions with a conse quent decrease in the melting temperature without much affecting the nemati c range. These compounds exhibit a rich solid polymorphism which is certain ly related to the effect of the conformations of the lateral substituent on the molecular arrangment in the solid phase. Some preliminary NMR experime nts on the nematic phase indicate that the molecular long axis coincides wi th the core axis, whereas the para-axis of the lateral fragment makes an an gle close to the magic angle with respect to the molecular long axis.