Intermolecular and intramolecular reorientations in nonchiral smectic liquid-crystalline phases studied by broadband dielectric spectroscopy

Molecular dynamics has been studied by broadband dielectric relaxation spec troscopy in the Sm-A, Sm-B, and Sm-E phases (Sm denotes smectic) of a homol ogous series of nonchiral stilbenes. An assignment of modes is presented ba sed on their dependence on temperature and molecular length, and, as far as they obey the Arrhenius law, their activation energy has been determined. In general, reorientations of entire molecules around their short axis are active, whereas reorientations of entire molecules around their long axis a re locked out in the Sm-E phase of shorter homologs, yet intramolecular reo rientations of polar sites have been established. Strong evidence is presen ted for an interdependence of reorientations of entire molecules around the short and long axes within the biaxial Sm-E phase of longer homologs.