SYNTHESIS, MESOMORPHIC PROPERTIES AND CRYSTAL-STRUCTURE STUDIES OF A CHIRAL FERROELECTRIC LIQUID-CRYSTAL SERIES

A new series of chiral mesogens: (R) 4-( 1-methylheptyloxycarbonyl)phe nyl 4-(4-alkyloxyphenyl)ethylylbenzoates-has been synthesized. All mat erials are mesomorphic and the liquid crystalline properties were char acterized by optical observation, DSC and electro-optical measurements . They display SmA and ferroelectric SmC phases at low temperatures. One of them, the nonyloxy derivative, exhibits the SmC(alpha) phase, present in different 'antiferroelectric' series. This behaviour is con firmed by mixture studies. Furthermore one compound of the series, the heptyloxy derivative, C37H48O5 crystallizes in the P-21 space group ( Z = 2) with the following parameters: a = 8.497 (1), b = 5.490 (1), c = 36.148 (4) Angstrom with beta = 92.72 (1)degrees. The final R and wR reliability factors were equal to 0.109 and 0.124, respectively; the goodness of fit was equal to 3.0. The whole molecule is L-shaped with the long chiral chain almost perpendicular to the core moiety as obser ved for several compounds showing an antiferroelectric mesophase. In t he crystal, the molecules related through the 2, axis, located at z = 0.5, give an antiparallel smectic C-like arrangement. The thickness of the sheets is equal to the c parameter, with a tilt angle close to 35 degrees. There are strong intersheet interactions between the chiral chains related through the 2(1) axes located at z = 0 and 1.