C-13 and H-2 NMR study of structure and dynamics in banana B-2 phase of a bent-core mesogen

In this paper, the difficulty in orienting the B-2 phase of the banana mesogen 1,3-Phenylene-bis 4-[4-(10-undecenyloxy)- benzoyloxy] benzoate ( Pbis11BB) in a relatively high magnetic field is reported based on some observations using both C-13 and H-2 NMR. H-2 NMR spectra recorded for the two labeled isotopomers of Pbis11BB in the isotropic and B-2 phases are shown here. Preliminary results on the deuteron spin-spin relaxation (T-2) data are reported at 61 MHz in order to underline the peculiar slow dynamics of banana-shaped liquid crystals (BLC), and these results are discussed in the framework of recent studies on similar BLC. The molecular structure and dynamics in the B-2 and crystalline phases are also studied by C-13 solid-state NMR techniques. The results also point to the slow dynamics in the B-2 phase of Pbis11BB. In particular, two-dimensional MAS exchange experiment has been performed to shed light on the molecular conformation structure of the five-ring banana core in the crystalline phase of Pbis11BB, and to compare with that of quantum mechanical calculations reported in the literature.