¹³C and²H NMR study of structure and dynamics in banana B₂ phase of a bent-core mesogen

In this paper, the difficulty in orienting the B₂ 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 ¹³C and ²H NMR. ²H NMR spectra recorded for the two labeled isotopomers of Pbis11BB in the isotropic and B₂ phases are shown here. Preliminary results on the deuteron spin-spin relaxation (T₂) data are reported at 61 MHz in order to underline the peculiar slow dynamics of bananashaped liquid crystals (BLC), and these results are discussed in the framework of recent studies on similar BLC. The molecular structure and dynamics in the B₂ and crystalline phases are also studied by ¹³C solid-state NMR techniques. The results also point to the slow dynamics in the B₂ 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.