Design,Synthesis And Characterization Of Blue-Emitting Dendritic Thermal Activated Delayed Fluorescence Materials

As one of the three primary colors（Red,Blue and Green）for organic light-emitting diodes（OLEDs）,the development of blue-emitting organic electroluminescent materials is of great significance for promoting the commercialization of OLEDs in the fields of flat panel display and solid-state lighting.In recent years,the development of high-efficiency thermally activated delayed fluorescence（TADF）materials based on low-cost solution processing processes has received increasing attention from academia and industry.Dendrimers bear well-defined molecular structure and good solubility,combining the advantages of small molecular materials and polymer materials,and have gradually become an important class of organic electroluminescent materials.Therefore,this thesis is focusing on dendritic host materials and dendritic blue-emitting TADF materials for the development of efficient solution-processed blue-emitting TADF OLEDs.The main contents are as follows:（1）Dendritic host materials,D1-OBu and D2-OBu,were developed using non-conjugated adamantane as the central core,carbazole with good hole transport properties as the branches,and n-butoxy with strong electron donating ability as the surface groups.By adjusting electron donating ability of the surface groups（from tert-butyl groups to n-butoxy groups）and the generation of carbazole dendrites（from the first generation to the second generation）,the regulation of the highest occupied molecular orbital（HOMO）energy levels is achieved while maintaining high triplet energy levels（>2.80 e V）.Among them,the HOMO energy level of D2-OBu is-5.19 e V,which can effectively reduce the hole injection barrier from the anode to the light-emitting layer.Using D2-OBu as host material and blue-emitting multiple resonance TADF emitter as dopants,blue electroluminescence with full width at half maximum of 30 nm,turn-on voltage of 3.1 V,maximum external quantum efficiency of 14.7%and CIE coordinates of（0.12,0.22）were achieved for solution-processed OLEDs.While for green multiple resonance TADF OLEDs,full width at half maximum of 42 nm,turn-on voltage of 2.8 V,maximum external quantum efficiency of 24.2%and CIE coordinates of（0.20,0.67）were obtained.（2）Using xanthene as bridging unit,triazine at 1-position as acceptor and carbazole dendrites at 9-position as donor,we designed and synthesized through space charge transfer（TSCT）blue-emitting TADF dendrimers D1Cz-TRZ and D2Cz-TRZ.Spatial separation of electron clouds between the donor and the acceptor can be achieved based on this U-shaped molecular design,which is beneficial for obtaining small singlet-triplet energy level difference(ΔE_ST)and realizing TADF emission.TheΔE_ST for D1Cz-TRZ and D2Cz-TRZ are 0.06 e V and 0.03 e V,respectively.When 10 wt%D1Cz-TRZ and D2Cz-TRZ were doped into m CP（1,3-di-9-carbozolylbenzene,host material）,blue emission at 451 nm and466 nm were obtained,respectively.The photoluminescence decay curves showed nanosecond prompt fluorescence and microsecond delayed fluorescence,indicating the TADF feature of D1Cz-TRZ and D2Cz-TRZ emission.