DETERMINATION OF ORIENTATIONAL ORDER PARAMETERS IN LIQUID-CRYSTALS FROM TEMPERATURE-DEPENDENT C-13 NMR EXPERIMENTS

We have shown that natural abundance C-13 NMR of solutes in liquid cry stals may be used to obtain order parameters from a series of temperat ure-dependent measurements even with limited information on the carbon shift tensors. A procedure for simultaneously analysing data at the v arious temperatures is proposed. We have obtained the ordering matrix as a function of temperature for various biaxial (D2h) solutes: pyrene , perylene, naphthalene, anthracene and for one effectively uniaxial p robe (triphenylene), in the nematic mixture ZLI-1167. We compare these results with deuterium data where possible and we also provide estima tes of the chemical shift tensors for perylene and anthracene, where s olid-state data are, as yet, unavailable.