Synthesis And Properties Of Difluorooxymethylene-bridged Bentcore Liquid Crystals

Bent-core liquid crystal has become a new branch of thermotropic liquid crystals after the rod-like and disc-like liquid crystal. The molecular structure of bent-core liquid crystal is bent. Because of the bent-shaped molecular structure,bent-core liquid crystal has a lot of unique optical and electrical properties which are very different from the conventional rod-like liquid crystal. In recent years,most of bent-core liquid crystals are based on substituted resorcinol and 1,3,4-oxadiazole as the central bent-core and-COO-,-N=N-,-C=N- as the linking group. These bent-core liquid crystals commonly have high melting point, high nematic transition temperature and narrow temperature range of nematic phase,which bring about the result that the bent-core liquid crystals can not be used in practical application. Synthesizing the new type of bent-core liquid crystals with low melting point,low nematic transiation temperature and wide temperature range of nematic phase has become a hot research field.In this paper, we designed and synthesized two types of novel bent-core liquid crystal compounds 10a~10g and 11a~11c, which were based on2,5-disubstitueted-1,3,4-thiadiazole and 2,5-disubstitueted-1,3,4-oxadiazole as the central units,difluorooxymethylene(-CF2O-)as the linking group and straight alkyl as the terminal chain. The chemical structures of the target compounds were confirmed by IR, 1H NMR, 13 C NMR, 19 F NMR and MS, and their transition temperatures and phase textures were investigated by using differential scanning calorimetric(DSC) and polarizing optical microscopy(POM). The result suggested that all of the target compounds had right chemical structure. In addition,all of the target compounds exhibited nematic phase and exist wide temperature range of nematic phase, the widest range of nematic phase was 92.74℃(compound 10a).The bent-core liquid crystals based on thiadiazole compared with that based on oxadiazole had higher melting point and wider range of liquid crystal phase. In comparison with the reported ester-bridged bent-core liquid crystals,difluorooxymethylene-bridged bent-core crystals prepared in this paper had much lower melting point and nematic transiation temperature, which indicated thattaking difluorooxymethylene as the linking group of the bent-core liquid crystal molecules could lower melting point and nematic transiation temperature. This result could provide research materials and theoretical basis for designing novel low-melting point bent-core liquid crystals.