Unusual dynamic behaviour in the isotropic phase of banana mesogens detected by 2H NMR line width and T2 measurements

In this work the first experimental observation of a peculiar behavior in the isotropic phase of liquid crystals by means of H-2 NMR is reported. In particular, two five-ring banana-shaped mesogens, the 1,3-phenylenebis-{4,4'-(11-undecenyloxy)benzoyloxy}benzoate (Pbis11BB) and its 4-chloro homologue (CIPbis11BB), selectively deuterium labeled on their central rings, are the subject of our investigation. The dynamic behavior of the two liquid crystals was studied in their isotropic phases and in the nematic phase of CIPbis11BB by means of H-2 NMR line width and spin-spin relaxation time (T) analysis. The results obtained reveal that the unusual line broadening observed in the H-2 NMR spectra in the. isotropic phase, even far above the isotropic phase-mesophase transition, has a homogeneous nature. thus indicating the presence of reorientational motions much slower than in conventional isotropic liquid-crystalline phases.