NEMATIC COMPOUNDS CONTAINING A 4-UNIT LINKING GROUP AND THE ORDER PARAMETERS OF THE MESOGENIC CORE

Eight compounds in a homologous series of liquid crystalline -n-alkoxy phenyl-3-(4-n-butylphenyl)-2-propenimines were synthesized. All member s of this series exhibit an enantiotropic nematic phase, which is quit e unusual for compounds containing a four-unit conjugated link. The or der parameters of different fragments (two phenyl rings and the four-a tom link) in the three related compounds were studied by 2D carbon-13 nuclear magnetic resonance with variable angle sample spinning. The te mperature dependence of the local order parameters were determined usi ng these data and the C-13 chemical shifts measured as function of tem perature. The order parameter of the ring bearing the ethylenic double bond is slighty larger than that of the ring bearing the imine group. The four-unit link was found to be quite rigid in the nematic phase. Assuming an average geometry, the major axis of the mesogenic core was found to make an angle of 4.1 +/- 1.1-degrees with respect to the par a axis of the ring bearing the ethylenic double bond.