Study On D-A Superlattice And Photoelectric Properties Based On Triphenylene And Perylene

Molecular engineering offers the possibility of obtaining a series of new molecules with high performance.The most typical example is the"molecular heterojunction",which is achieved by covalently linking two groups such as electron donor（D）and electron acceptor（A）.The discotic liquid crystal molecules exhibited two distinct and active charge transport pathways through the formation of 1D columns."Molecular heterojunction"achieves excellent donor and acceptor morphology,achieving excellent charge transmission performance and providing an ideal structure for building solar cells.Based on the previous topic group,5D10An（n=4,5,6）and 5Dm A4（m=5,6,8,9）molecules were synthesized.The optical properties were analyzed by UV-Vis absorption spectroscopy.Compared with the monomer,the compounds were absorbed in ultraviolet and visible light regions,which expanded the spectral absorption range.The liquid crystal properties of the compounds were analyzed by POM、DSC and 1D WAXD.The liquid crystal properties of the compounds were all normal temperature liquid crystal,with a wide range of liquid crystal.In addition,the liquid crystal phase structure changed with the increase of temperature.The phase structure of the compound was further studied by SAXS and 2D WAXD.It was found that the long-range ordered superlattice structure could be formed when the compounds with the carbon number of linkages are multiples of 5,which was exactly the length of triphenylene pentyloxyl side chain.Based on the analysis of two-dimensional X-ray diffraction lattice with different orientations,it is confirmed that 5D5A4 and 5D10A4 formed a rare 9₁ helical superlattice structure with an angle of 40°.By using density functional theory（DFT）to simulate the dipole moment and surface electrostatic potential energy（ESP）,and using X-ray diffraction to simulate the electron density map（EDM）to reasonably infer the formation of 2D superlattice structure of D-A molecules.The spiral superlattice models of 5D5A4 and 5D10A4molecules were reconstructed.Subsequently,we synthesized 5D5An（n=5,6）molecules,which proved that both compounds were normal temperature liquid crystals and formed a highly orderly rectangular columnar plastic phase.The formation of superlattice structure was proved by SAXS and 2D WAXD analysis.The charge carrier mobilities were characterized by TOF method,they exhibited highly efficient ambipolar charge-transport properties.Among them,the charge carrier mobility of 5D5A4 and 5D10A4 can reach the order of 10^-3cm²V^-1S^-1,which is due to 5D5A4 and 5D10A4 formed a spiral superlattice structure,and the molecules were stacked more tightly and orderly,which promoted its charge transmission.The superlattice 5D5An（n=4,5,6）and 5D10An（n=4,5,6）molecules were compared.The 5D5An（n=4,5,6）series formed a rectangular columnar plastic crystal phase,and the clear point of the molecules was about 25℃higher than that of the 5D10An（n=4,5,6）series molecules on average.The enthalpy corresponding to the liquid phase transition and the isotropic state is much higher than that of the5D10An（n=4,5,6）series.Besides,the enthalpy corresponding to the liquid phase transition and the isotropic state is much higher than that of the 5D10An series.By comparison,it can be seen that 5D5An（n=4,5,6）liquid crystal has a wider range and requires higher energy to destroy the structure.Compared with 5D10An（n=4,5,6）series,it is more orderly and the structure formed is more stable.