Penta- and hexa-substituted phenanthrenes and penta-substituted benzo[
c]-phenanthrenes have been synthesized; these exhibit columnar phases
and are electrically switchable when bearing chiral side chains. The l
iquid crystalline and electro-optical properties are described. A stro
ng tri-state switching behaviour is observed with the phenanthrene der
ivatives. A helical phase structure, responsible for this switching be
haviour, is proposed and the possible mechanism of the columnar phase
switching process is discussed.