SYNTHESIS OF HIGHLY CHIRAL MULTISUBSTITUTED BINAPHTHYL COMPOUNDS AS POTENTIAL NEW BIAXIAL NEMATIC AND NLO MATERIALS

A number of multi substituted binaphthalene compounds were synthesized in an attempt to obtain a highly chiral biaxial nematic (N-b) phase o r a good NLO material. Introduction of two pairs of substituents into the binaphthalene molecule [GRAPHICS] with one of these being a nitril e group and R = C-10 was successful but neither this compound nor the above esters showed any mesophases. Introduction of additional pairs o f substituents proved to be difficult. Friedel-Crafts acylation to add a third pair through a ketone gave complicated mixtures of products o btained by cleavage of the ether followed by acylation. Bromination, w hich could lead to either the necessary nitrile substituent or esters via the acid obtained from the nitrile generally gave mixtures of brom ides as expected. Some of these could be separated by chromatography a nd successfully converted to the nitrile. However, attempts to hydroly ze these nitrile groups usually gave mixtures of various products of i ncomplete hydrolysis producing compounds that did not have the appropr iate substituents for observing mesophases. No mesophases were observe d in any of the binaphthalene compounds prepared. The (R)-(+) optical isomer of the above nitrile with R = C-10 was also prepared to study i ts potential use as a chiral dopant. This isomer had a melting tempera ture below that of the racemic material indicating that the latter is a racemic compound. A few mixture studies using primarily the racemic dopant with known liquid crystals indicated that low percentages (< 10 per cent) of this dopant gave good mixtures. The best mixtures were o btained using a cyanobiphenyl (80CB) host which showed an enhanced nem atic phase. Mixtures of a small amount of the chiral dopant in room te mperature nematics gave highly coloured cholesteric (twisted nematic) phases.