NMR study of a phasmid-like liquid crystal

Carbon-13 NMR measurements of the chemical shifts are reported as a function of temperature for a semi-phasmidic molecule 4-(2,3,4-tridecyloxy-phenylazo)-benzoic acid (TDPABA). The data indicate a dimer structure in the solution and suggest a similar structure also in the nematic phase, which is consistent with it being a phasmid-like liquid crystal. The orientational order parameters are derived in the nematic phase based on the carbon shielding tensors calculated by Density Functional Theory. The nematic order parameter Szz is found to be (relatively) higher for TDPABA than that found in a typical calamitic liquid crystal, likely due to its underlying columnar phase.