Design,Synthesis And Properties Of Ketone-based Thermally Delayed Fluorescent Materials

Organic light emitting diodes?OLEDs?,as a new generation of display technology,are widely applied in many fields such as lighting and displays.Thermally activated delayed fluorescence?TADF?materials,as the third generation of light-emitting materials of OLED,are widely investigated by the scientific and industrial fields because of their advantages such as low synthesis cost and strong designability.Ketone groups are widely used in the design and synthesis of TADF materials due to their strong electron-withdrawing capabilities.In this thesis,a series of highly efficient TADF materials are designed and synthesized.The results are as follows:?1?Based on the ketone group chromenone?CZB?,the compound 3-?4-?10H-phenoxazin-10-yl?benzoyl?-4H-chromen-4-one?CZB-PXZ?was synthesized,and the chemical and physical properties were characterized and analyzed.the smaller singlet-triplet splitting(?E_ST)of CZB-PXZ,which makes the intersystem transition easier;due to the higher intersystem transition rate and singlet radiation rate,the PL quantum yield of the thin films doped with CZB-PXZ is up to 93%;weak intramolecular and intermolecular forces in CZB-PXZ molecular exhibit concentration-insensitive properties.Within the doping range of 1 wt%to 10 wt%,the OLED devices show similar emitting properties.The exciton utilization rate is over 75%.When the doping concentration is 5wt%,the device achieves the best performance.The external quantum efficiency,the current efficiency and the power efficiency are 22.0%,66.5 cd/A,and 70.6 lm/W.At the low doping concentration of 1 wt%,an external quantum efficiency of more than 20%could still be achieved,which indicates that the energy is completely transferred and utilized,and efficient device fabrication is achieved.?2?The compounds 3-?4-?9H-carbazol-9-yl?benzoyl?-4H-chromen-4-one?CZB-Cz?and 3-?4-?3,6-di-tert-butyl-9H-carbazol-9-yl?benzoyl?-4H-chromen-4-one?CZB-TCz?were synthesized based on the ketone group chromenone?CZB?.The partial separation of the highest occupied molecular orbital?HOMO?and the lowest unoccupied molecular orbital?LUMO?results from the smaller?E_ST between the two molecules,which enables charge transfer within the molecule and the possibility of anti-systemic migration.At the same time,the partial overlap of molecular orbitals leads to the existence of local excited states of molecules.Under the electroluminescent condition,two emission peaks were appeared,and the characteristics of white light could cover a whole range of visible light,that is,single-molecule white light.Among them,the exciton utilization rate of devices based on CZB-TCz exceeds 25%,indicating that the materials have TADF emission characteristics.The dual emission peaks make the device have good white light properties.CZB-Cz and CZB-TCz based devices were correspond to the maximum CRI of 78 and88 respectively,of which white light with CZB-TCz is warm white light.In summary,this dissertation uses the new ketone group CZB to design and synthesize two TADF materials,which enriches the types of materials,prepares a series of high-performance OLED devices,and describes the material and device performance from the structure point of view,and provides ideas for the research of ketone TADF materials.