Effect Of Center Unit On The Properties Of Bent-Core Liquid Crystals

In this thesis we synthesized three series of bent-core liquid crystals with 1,3,4-thiadiazole as the center unit, their liquid crystalline properties were studied with DSC combining with the POM observation, it was found all of these thiadiazole compounds exhibited N phase. Among them, the symmetric thiadiazole derivatives with three benzene rings and alkyl terminal chains have melt at 100℃, while the clearing temperatures are lower than 165℃; symmetric five benzene ring thiadiazole ester compounds have high melting points, and the clearing temperatures are more than 360℃. The clearing temperatures of the unsymmetric thiadiazole molecules with allyl terminal chains are also high, but the N phases have a very wide temperature range (> 90℃).Besides, two types of compounds with 4-substituted resorcinol as the central unit were synthesized, and their liquid crystalline properties were studied by DSC and POM. It was found that the molucules with 4-nitroresorcinol central unit exibited smectic phase only by cooling, none of liquid cryatalline phase was found by heating, the results indicated that the introducing of nitro group would greatly reduce the liquid crystalline stability of the bent-core liquid crystals, and nematic phase was disappeared; the compounds with 4-cyanoresorcinol center uint exibit excellent properties, and they will be further studied.