Synthesis,Characterization And Application Of Cross-linkable Hole-transporting Materials In OLED Devices

Hole-transporting materials（HTMs）are widely used in organic optoelectronic devices.As an analog of triphenylamine,which is an important building block of HTMs,planar triphenylamine has attracted much attention in recent years because of its unique structure and properties.Cross-linkable HTMs can be used to overcome the interfacial mixing issues associated with the solution processing of multilayer devices.Five new planar triphenylamine-based HTMs DTPA1-5 were designed and synthesized.DTPA1-5 which bearing cross-linkable vinyl and trifluorovinyl groups are N-heterotriangulene derivatives.The chemical structure of target compounds DTPA1-5 was characterized by ¹H NMR,¹³C NMR and HRMS spectroscopy.The optical properties of DTPA1-5 were studied by UV-Vis spectroscopy and fluorescence spectroscopy.DTPA1-5 show high fluorescence quantum yields（0.67-0.91）in dichloromethane solution.The electrochemical properties of DTPA1-5 were studied by cyclic voltammetry.The results show that the oxidation potentials of DTPA1-5 are lower than that of their parent planar triphenylamine.The results of DFT calculations reveal that the HOMOs are mainly located on the planar triphenylamine core and the LUMOs are mainly located on the peripheral phenyl substituents.Furthermore,the thermotropic properties of DTPA1-5 were investigated by thermogravimetric analysis and differential scanning calorimetry.DTPA1-4 exhibit high thermal stability and thermal cross-linkable properties.OLED devices were fabricated as the configuration of ITO/HTL/Alq₃/Li F/Al and cross-linkable DTPA1-4 were used as hole-transporting layers.The influence of cross-linking on device performance was also studied.Hole-transporting material DTPA4 shows best performance.Device 7containing DTPA4 as hole-transporting layers exhibits turn-on voltage of 3.0 V,maximum luminance of 15810 cd·m^-2,maximum current efficiency of 3.61 cd·A^-1 and maximum power efficiency of 2.54 lm·W^-1.