Adamantane and Heptazine Based Discotic Liquid Crystals


Supervisor:yang hong


Degree Year:2017





A series of new discotic liquid crystals(DLCs)containing an adamantane central unit with the four bridgehead positions partially or fully decorated with different numbers(1-4)of 3,4,5-tris(dodecyloxy)phenyl carbamoyl groups are designed and investigated carefully to explore the structure-property correlations.The molecular structures and mesomorphic properties of the DLCs are characterized by ’H-NMR,13C-NMR,IR,UV-Vis,POM,DSC and XRD.It is found that the mesophase symmetry and thermal stability are extremely dependent on the structures of the adamantane derivatives.No mesophase is observed for the 1-adamantanecarboxylic acid derivative ADLC1,while two different mesophases are observed for ADLC2,a 1,3-disubstituted derivative functionalized with two 3,4,5-tris(dodecyloxy)phenyl carbamoyl groups at two symmetric bridgehead positions.At lower temperature,ADLC2 exhibited rectangular columnar phase which switched to the square columnar phase with a wide range of thermal stability.Similarly,hexagonal columnar mesophase is observed for the bridgehead trisubstituted adamantane molecule ADLC3.Interestingly,the fully bridgehead-functionalized 1,3,5,7-tetrasubstituted adamantane compound ADLC4 completely lost liquid crystallinity.Heptazine is the fundamental structural and functional unit of graphitic carbon nitrides(g-CN)and has a 7r-conjugated planar symmetry with semiconducting properties.Molecular self-assembly is one of the key factors to drive the electronic behavior of π-conjugated organic molecules.To enhance the semiconductivity,heptazine is decorated at its active sites with 2,3,5-tris(dodecyloxy)aniline to get well-organized columnar packing.A novel heptazine-core room-temperature discotic liquid crystal(HDLC)with hexagonal columnar geometry is discovered.The molecular structure and mesomorphic properties of HDLC are investigated by 1H-NMR,13C-NMR,IR,POM,DSC,and XRD.Photophysical and electrochemical properties of HDLC are studied by UV-Vis/fluorescence spectroscopy and cyclic voltammetry,respectively.The energy band gap of HDLC estimated from CV at room temperature is 1.63 eV,which is much narrower than the previously reported band gap for heptazine derivatives.This decrease in the energy band can be attributed to the particular designing of HDLC for columnar packing.As a columnar liquid crystal providing a smooth path to the charge transport,HDLC with such a narrow energy band gap may find applications in organic electronics.