Design,Synthesis And Properties Of High-Efficiency Red And Near-Infrared TADF Materials Based On Rigid And Planar Receptor Units

Organic light-emitting diode(OLED)are gradually occupying a dominant position in the field of display and lighting due to their advantages of self-illumination,wide color gamut,lightness and low cost.Since the performance of the devices are determined by the properties of materials,the development of materials with high luminous efficiency has been the focus of research.Because of using no expensive heavy metals,thermally activated delayed fluorescence(TADF)materials can greatly reduce production costs.More importantly,due to its small ΔEST,the utilization of triplet excitons is greatly improved,the maximum internal quantum efficiency of the device can reach 100%theoretically.At present,blue and green OLEDs have shown excellent performance.However,the performance of red and near-infrared(NIR)devices are still poor,because according to the energy gap law,red and near-infrared TADF materials with narrow bandgaps typically suffer more serious non-radiation energy loss,which will lead to their efficiency much lower than blue and green materials.Hence,there are enormous challenges in designing highly efficient red and near-infrared TADF materials.In this paper,a series of red and near-infrared TADF materials based on different rigid and planar acceptor units were designed and synthesized,and the corresponding OLED devices were prepared.We systematically studied the design,synthesis and properties of the materials.1.The red TADF material AZA-TPA was designed and synthesized with azaacene as the acceptor unit and triphenylamine as the donor unit.From the perspective of molecular structure,the introduction of cyano group in the ortho-site of TPA leads to a wide separation of HOMO and LUMO,and a small ΔEST,which greatly improves the utilization of triplet excitons.The non-radiative transition is inhibited by the rigid skeleton,which results in a high PLQY of 94.6%.Moreover,due to its linear and planar shape,AZA-TPA showed a high Θ//of 90%.Therefore,the OLED based on AZA-TPA exhibited a superior external quantum efficiency of 41.3%at 610 nm.2.The red TADF material TH-PO-TPA was designed and synthesized with dithiophenazine as the acceptor unit and triphenylamine as the donor unit.In this work,the nonradiative transition rate of the material was significantly reduced by integrating the donor unit and the acceptor unit with a rigid and planar skeleton.Additionally,the auxiliary group diphenylphosphine oxide is introduced to increase the molecular aspect ratio,which can not only improve the light out-coupling efficiency of the materials,but also enhance the external quantum efficiency of the devices.As a result,the OLED based on TH-PO-TPA showed an EQE of 25.56%at emission peak of 637 nm.3.The near-infrared TADF material FCNPZ-TPA was designed and synthesized with dipyridinophenazine as the acceptor unit and triphenylamine as the donor unit.The introduction of four cyano groups at positions 3,6,10,13 increases the electronwithdrawing property,the two adjacent triphenylamine with large volumes exhibit excellent electron-donating ability.Distorted D-A configurations caused by steric hindrance will reduce aggregation-caused quenching(ACQ),while at the same time,this will lead to a small ΔEST.In addition,by introducing strong donor-acceptor unit into the molecular skeleton,the emission of FCNPZ-TPA can reach the near-infrared region.When FCNPZ-TPA was doped in the CBP,benefited from the rigid skeleton of the material and the small ΔEST,the device exhibited the external quantum efficiency of 8.01%at 742 nm.