Thermal and Dielectric Properties of Liquid Crystals with a Coumarin Skeleton

In order to examine the liquid crystalline properties of coumain, 3-X- and 7-Y-substituted coumarins where X=cyano and n-alkoxycarbonyl, and Y=4-n-alkyl- and 4-n-alkoxybenzoyl, 4-alkoxycinnamoyloxy, 4′-alkyl- and 4′-alkoxy-4-biphenylylcarbonyloxy, and 4-(4-alkoxybenzoyloxy)benzoyloxy (4) groups have been prepared. The compounds with X=alkoxycarbonyl group tend to exhibit strong smectic properties, and compounds with X=cyano exhibit stable nematic phases, whereas the coumarin core seems to facilitate a lateral separation of molecules in the mesophase due to its large molecular breadth. The heptyloxy homolog of 4 exhibits a reentrant behavior of the C–Nre–SA–N–I type. The thermal properties are discussed in terms of the polarity and polarizability of coumarin, and the molecular structure. The dielectric properties of the compounds have also been examined and discussed in terms of the polarity of the coumarin core.