Synthesis Of Novel Thermally Activated Delayed Fluorescence Materials And The Applications In Photoelectric And Sensing Fields

Thermal activated delayed fluorescent materials（TADF）are the third generation of organic fluorescent materials after the first generation of traditional organic fluorescent materials and the second generation of organic phosphorescent materials,because of its smaller between singlet and triplet energy difference,can form a small electronic exchange,at room temperature,excitons from the triplet state can be returned to the singlet state by the reverse intersystem crossover process（RISC）,then the singlet state is transferred back to the ground state by exciton radiation,so that the exciton utilization can reach 100%.TADF material achieves the acquisition of triplet excitons in pure organic molecules for electroluminescence,and through the design of molecular structure,solves the contradiction between the large radiation rate constant of S₁ excited state and the guarantee smallΔE_ST.TADF material has made rapid progress in the past few years as a emitter,and is considered as the next generation of OLED technology.TADF OLEDs have achieved high device performance comparable to phosphorescent OLEDs constructed with organic complexes containing precious metals.Although most of the research about the electroluminescent application,there are a lot of novel materials with TADF properties indicated that the development prospect of the potential of other applications,such as TTA sensitizer,organic UV photodetectors,fluorescent probes and mechanical light discoloration,etc.,however,about TADF materials research and development is still in its infancy.Therefore,despite the rapid development of TADF research,there are still many possibilities for exploration.In chapter 2,two symmetrically packaged blue TADF molecules 4Cz-SO and 43Cz-SO were designed and synthesized,which were easy to synthesize and could be used in solution treatment.Carbazole groups were introduced by alkyl chain.The research shows that,these two materials have excellent solvent resistance and can be prepared by solution method,which solves the problems of small area,long time consuming and high cost of OLED preparation.On the other hand,the blue 4Cz-SO and 43Cz-SO molecules encapsulated by carbazole guarantee the stability of TADF material.Meanwhile,the introduction of alkyl chain makes the structure highly distorted,resulting in smaller overlap between HOMO and LUMO,smaller energy difference(ΔE_ST)between triplet and singlet states,and faster RISC,TADF features have been improved.In addition,the molecular packaging design not only promotes the utilization and energy transfer of excitons,but also ensures the stable charge injection and transfer of luminescent layer,inhibits the concentration quenching,reduces the loss of device efficiency,and improves the luminescent efficiency.At the same time,the experimental results showed that reasonable introduction of the donor can improve the efficiency of the exciton,and excessive donor may cause the quenching of the exciton,resulting in the efficiency of the device.DSC test results showed that both 4Cz-SO and 43Cz-SO have higher glass transition temperatures（Tg=198℃）.Theoretical calculation shows that both of these two materials have higher triple state energies（T₁=2.78 e V and 2.79 e V）.The energy difference between singlet state and triplet state is small for RISC process,and it has excellent TADF characteristics.Atomic force microscopy test results show that the film forming performance of these two materials is very good,observe the formation of uniform amorphous film,is the premise of preparing perfect OLED devices.The electroluminescence performance test shows that 4Cz-SO has better self-subject luminescence performance than 43Cz-SO,just because of the contribution of appropriate donor introduction,and the two materials were tested as the main doped TADF blue light object to optimize the study of blue light luminescence performance,experimental results show that,4Cz-SO is much better than 43Cz-SO as the main material for optimizing blue light emitting devices.The maximum brightness of the two materials is 8900cd/m² and 2200 cd/m²,respectively.The maximum CE and maximum external quantum efficiency（EQE）of blue light emitting devices optimized based on 4Cz-SO are 30.1 cd/A and 17.6%,respectively.The maximum CE and EQE of the blue ray device optimized based on 43Cz-SO are18 cd/A and 8.8%,respectively.The above conclusions are verified again.In addition,the performance of hybrid WOLED was further studied by using 4Cz-SO molecule.Experimental results show that the brightness of 4Cz-SO doped white light OLED can reach 12000 cd/m²,and the maximum CE and maximum external quantum efficiency（EQE）are 30.6 cd/A and 18.1%,respectively,which are higher than that of traditional materials such as MCP.There has been a huge efficiency improvement.The effect of TADF as additive on perovskite device is studied in chapter 3.We introduced a TADF dendritic macromolecule Cz-4Cz CN as a functional additive of perovskite emission layer.Systematic thermal and optical physics and morphology studies show that Cz-4Cz CN is an effective exciton recovery additive because it meets the following conditions:good solubility in polar solvents;High energy triple energy inhibits energy reverse transfer;Amorphous state,ensure the film quality;SmallΔE_ST,facilitating 100%exciton utilization.The results showed that the optimized quasi-two-dimensional Cs Pb Br₃:Ammonium phenyl ethylate bromide（PEABr）based Pe LEDs device has a low switching voltage of 3.0 V and a high brightness of 18000 cd m^-2.The maximum current efficiency and external quantum efficiency are 39.0 cd A^-1 and 10.1%EQE,respectively,which are almost 5 times higher than those of additive free control devices.In addition,the half-life of the device is increased by 2 times after TADF dendrimers are added.We also designed and synthesized the parent additive Cz-4Cz Ph with similar molecular structure but without TADF characteristics,and explored the mechanism and action of TADF additive.It was found that 54%of the improvement in device efficiency was due to defect passivation and 46%to recovered energy.This study for the first time demonstrates that self-encapsulated TADF dendrimer is a promising additive to improve the performance and stability of Pe LEDs devices.The fourth chapter of this thesis mainly studies the application of TADF materials in the detection of heavy metals in the fluorescence sensor.We designed and synthesized a fluorescent probe TPA-SO-OH,which has good TADF properties and specificity for the detection of Fe³⁺.TPA-SO-OH was constructed by using triphenylsulfoxide as luminescent unit and hydroxyl group as recognition group.The thermodynamic,photophysical and electrochemical properties of the probe were characterized.A smallΔE_ST of 0.16 e V was obtained in the low temperature phosphorescence spectrum,which ensures effective intersystem reverse crossover（RISC）of TADF materials.The fluorescence intensity of the probe was significantly increased by two times after nitrogen bubbling,which also confirmed the TADF feature.The probe has high Td and Tg,which are 323℃and 78℃respectively,indicating that it has good thermal stability.Ion competition experiments showed that the probe could detect iron ions with a binding ratio of 2:3.In addition,the probe has good fluorescence stability in different p H environments.In this study,TADF material was successfully used as a fluorescence probe for ion detection for the first time,which provides a new method for the development of fluorescence sensors.In this thesis,there are 60 figures,4 tables and 121 references.