Study On Two-dimensional Discotic Liquid Crystal Superlattice

A series of discotic liquid crystals based on hexapentyloxytriphenylene(HAT5)have been investigated where one out of the six ether side chains of a triphenylene core was replaced by an ester side chain and named for T5E1-T5E9.During the process of studying these compounds,the characteristic straight line defect of ordered columnar structure was identified by polarizing optical microscopy(POM)and liquid crystal state over a wide temperature range was obtained by differential scanning calorimetry(DSC).Basic phase structure and molecular arrangement were assigned by one-dimensional wide-angle X-ray diffraction(1D WAXD),small-angle X-ray scattering(SAXS),twodimensional wide-angle X-ray diffraction(2D WAXD)and transmission electron microscope(TEM).Combined with sharp and regular dots in 2D WAXD patterns and characteristic peaks at small angle in SAXS pattern which indicated the existence of superlattice,we proved that 2D superlattice formed from self-assembly of discotic molecules with a polar group via π-π stacking and dipole-dipole interaction.In conclusion,superlattice structure can be formed from discotic molecules via a hierarchical self-assemble process.First,three discs arranged together to form a small triangle lattice via the dipole-dipole interaction.Second,the triangle lattices stacked into a column via the π-π interaction.Third,three columns intended to form a hexagonal lattice via the dispersive force of soft alkyl side chains and finally the hexagonal correlated columns formed a long-range ordered hexagonal superlattice.In order to verify the effect of orientation on charge carrier mobility,their electron and hole mobilities were measured by time-offlight(TOF)device,among which the charge carrier mobility of T5E4 could achieve almost twice as that of HAT5.