Slow molecular reorientation in higher-ordered liquid crystalline phases of a homologous series of stilbenes

Reorientations of molecules in orthogonal smectic phases (SmA, SmB, and SmE) of a homologous series of stilbenes have been studied by broad band dielectric spectroscopy and their activation energies have been determined. The effect of the molecular length on the reorientation around a short and the long molecular axis is described in detail. The reorientation around the long molecular axis is locked out in the SmE phase of homologues with a short alkoxy chain length whereas the reorientation around the short molecular axis is always active. A change of the activation energy describing the reorientation around a short molecular axis is accompanied by a change of the relaxation frequency of the reorientation around the long molecular axis in the SmE phase. This coincidence compels evidence for a relationship between both reorientations in the higher-ordered biaxial smectic E phase.