Synthesis And Properties Ofβ-Substituent Tripheylene Based Discotic Liquid Crystals

A series of triphenylene esters T5E23,T5E27,T5E26 and T5E36 with two ester group at different substituent positions was successfully synthesized,where T5 refers to pentyloxy triphenylene,E refers to ethoxycarbonyl chain and 23,27,26 and 36 refer to the substituent positions of ethoxycarbonyl.Their chemical structures were confirmed by proton nuclear magnetic resonance（¹HNMR）,high resolution mass spectrum（HRMS）and Fourier transform infrared spectroscopy（FT-IR）.The mesomorphic properties were futher investigated by polaring optical microscopy（POM）,difference scanning calorimetry（DSC）and 1D Wide-angle X-ray diffraction（1D WAXD）.The results proved that all the four compounds exhibited hexagonal columnar phase but only T5E26 and T5E36 can maintain this mesophase to room temperature.Meanwhile,T5E36 showed phase transition when the temperature dropped to room temperature.With the help of 2D wide-angle X-ray diffraction（2D WAXD）and small-angle X-ray scattering（SAXS）,we can draw a conclusion that both T5E26 and T5E36 formed specific superlattice structures.The diffraction spots in wide-angle region and layer lines pattern obtained by shearing futher illustrated that T5E36 formed a rare helical superlattice structure.This helical superlattice structure was further studied by using transmission electron microscopy（TEM）and the diameter of the T5E36 particles was found to be at the nanometer scale.Ultimately,the bipolar charge carrier mobility was measured by the time-of-flight（TOF）method to be in the order of 10^-1cm²V^-1s^-1.At the same time,a series of main chain discotic liquid crystalline polymers T4P36-n based on3,6-substituent triphenylene derivatives was successfully synthesized,where T4 refers to butoxyl triphenylene,P refers to the main chain polymer,36 refers to the substituent positions and n refers to the number of methylene groups in the spacer.Their chemical structures were confirmed by proton nuclear magnetic resonance（¹HNMR）and Fourier transform infrared spectroscopy（FT-IR）.Gel permeation chromatography（GPC）was used to determine molecular weights（MWs）.The results confirmed that the spacer lengthes decisively influence the molecular weights.The polymers with even spacer lengthes were more likely to have low molecular weights due to cisoid conformation with higher activation energy.The mesomorphic properties were futher investigated by polaring optical microscopy（POM）,difference scanning calorimetry（DSC）and 1D Wide-angle X-ray diffraction（1D WAXD）.The results proved that all the four compounds exhibited hexagonal columnar phase.Nevertheless,only T4P36-8 and T4P36-9 showed two peaks which can be indexed to（002）and（102）plane in the wide-angle region.These peaks confirmed both T4P36-8 and T4P36-9 formed highly ordered hexagonal columnar plastic phase.These highly ordered dicotic liquid crystals made them more attractive in organic electronics.