NMR STUDY OF MOLECULAR CONFIGURATION AND ORDER IN A FLUORINATED-LIQUID-CRYSTALLINE SCHIFF BASE

The fluorine and proton spin resonances in the nematic-liquid-crystal state of terephthalbis(aminofluorobenzene) are studied using the method of moments. The second moment of the proton line has a large dependence on the molecular configuration as well as on the degree of molecular order. The fluorine second moment, on the other hand, has a negligible dependence on the configuration and is used to obtain a measure of the order. With the degree of order known, the second moment of the proton resonance is used to examine possible configurations the molecule may follow. The results rule out the possibility of a planar molecule as well as a molecule in which the aromatic rings and the -N=CH- linkage groups are allowed to rotate around their bonds in an unhindered fashion. Best agreement with the data is found for the case where the plane containing the linkage group makes a preferred angle near 20° relative to the plane of the terminal aromatic rings. The temperature dependence of the proton spectrum is also interpreted in terms of the molecular order.