SYNTHESIS, CHARACTERIZATION AND CRYSTAL-STRUCTURE OF MESOGENIC COMPOUNDS WITH AN ALKYLOXY AND A SEMI-PERFLUORINATED CHAIN - INFLUENCE OF THE ALKYLOXY CHAIN-LENGTH ON MOLECULAR ARRANGEMENT AND MOLECULAR-INTERACTIONS

This paper describes the synthesis and study of the mesomorphic proper ties (by DSC, microscopic observation and X-ray diffraction) of three new series of semi-perfluorinated liquid crystals: (2,2,3,3,4,4,4-hept afluorobutyloxycarbonyl)phenyl, ,2,3,3,4,4,5,5-octafluoropentyloxycarb onyl)phenyl, and ,6,7,7,8,8,8-tridecafluoro-octyloxycarbonyl)phenyl 4- (n-alkyloxy)benzoates. One compound of the second family crystallizes in the <P(1)over bar> space group with Z = 2. The molecule adopts a sl ightly bent conformation with a fully extended alkyloxy and semi-perfl uorinated chain in a smectic C-like structure. The comparison of the p resent structure is made with that of a similar compound of the first family with a longer alkyloxy chain (this latter crystallizes in the P 1 space group with two independent molecules in the unit cell). Compar ison of the molecular packing shows the importance of the chain length s in the molecular arrangement and molecular interactions in both stru ctures.