We have performed a structural study of the mesophases of some isomeri
c hexa-substituted phenanthrenes. Evidence for a new hexagonal columna
r mesophase with three columns per unit cell was found in a chiral iso
mer. Moreover, a rectangular columnar phase with four columns per latt
ice, similar to the low temperature mesophase of a hexa-substituted ru
figallol, ws found in a different material. The relations between the
structures and the electro-optical behaviour of the different mesophas
es are discussed.