Synthesis And Properties Of The Fluorinated Bent-core Liquid Crystals With 1,3,4-oxadiazole

In recent years,liquid crystal display technology has become the main direction of display area.the response speed of bent-core liquid crystal,which has excellent biaxial nematic phase,is much faster than the rod-like liquid crystal.What's more,it is one of the hottest areas of liquid crystals after the rod-like and disc-like liquid crystal.The bent-core liquid crystals,which have been reported,commonly have high melting point,high nematic transition temperature and narrow temperature range of nematic phase(?TN),which bring about the result that the bent-core liquid crystals can be hardly used in practical application.So it is one of the research hotspot to design and synthesize novel bent-core liquid crystal compounds with low melting point,low transition temperature and wide range of nematic phases.In this paper,we designed and synthesized three serial novel bent-core liquid crystal compounds ?1~?3??1~?3 and ?1~?3,which were based on 2,5-disubstitueted-1,3,4-oxadiazole as the central units,difluorooxymethylene(-CF2O-)as the linking group,the benzene with different position and number of fluorine atoms as the rigid arm and straight alkyl as the terminal chain;In addition,we have also synthesized two series bent-core molecules(?3~?7,?3 ~?7)with ten 2,5-bis(4-alkoxy-phenyl)-1,3,4-oxadiazole compounds.The chemical structures of the target compounds were confirmed by IR,1H NMR,13 C NMR,19 F NMR and element analyzer,and their transition temperatures and phase textures were investigated by using differential scanning calorimetric(DSC)and polarizing optical microscopy(POM).The result suggested that the target compounds had right chemical structure,and mostly compounds of series ?~? can show liquid crystal phase,however,the compounds of series?~? have no liquid crystal phase.Study on the impact of the liquid crystal phase change and the melting point by introducing fluorine atoms in the compounds.We find that a suitable position to introduce an appropriate amount of F atoms contributes to reduce the melting point of the liquid crystal compounds and broaden the nematic phase transition temperature range;Meanwhile,we also find that branched chains are introduced can greatly reduce the melting point of such compounds down to below room temperature on the end of the flexible chain,which provides creative and theoretical basis for the future to design new low-melting bent-core liquid crystals.At the same time,we preliminarily researched the optical properties by UV-vis spectrum and fluorescence spectrum as well.And we discovered that these compounds have a high fluorescence quantum yield,making such compounds possible to be used in the field of OLED.