NMR investigation of the dynamics of banana shaped molecules in the isotropic phase: a comparison with calamitic mesogens behaviour

The first translational self-diffusion NMR measurements in the isotropic phase of banana-shaped liquid crystals are reported. In this paper, two banana-shaped mesogens, having a similar molecular structure and showing a nematic phase, have been investigated by means of translational self-diffusion NMR, H-2 NMR spin-spin and H-1 NMR spin-lattice relaxation measurements in the isotropic phase. While H-1 diffusion and H-2 relaxation times reveal a peculiar slow dynamic behaviour of banana-shaped mesogens compared with calamitic mesogens, the H-1 relaxation times seem to be affected by fast dynamics only. The origin of these dynamic features is discussed in terms of overall and internal molecular motions, in the frame of recent speculations concerning the formation of molecular clusters or aggregates in the isotropic phase of banana-shaped liquid crystals.