Design,synthesis And Device Application Of Novel Asymmetric Disubstituted Fluorene Electroluminescentmaterials

Organic light emitting diode（OLED）has made great progress since its birth.The efficiency,brightness and life of its devices meet the commercial indicators.At present,OLED is still a research hotspot in the field of organic electronic display,and people’s pursuit of high-efficiency OLED materials has never stopped.So far,according to the classification of its luminescence mechanism,three generations of OLED series have been produced.The first generation of traditional fluorescent materials,the second generation of phosphorescent materials（PHOLED）and the third generation of thermally activated delayed fluorescent materials（TADF-OLED）.The first generation of traditional fluorescent materials only use singlet excitons,so its maximum internal quantum efficiency is limited to 25%;The second generation phosphorescent materials break the shackles of the maximum internal quantum efficiency of traditional fluorescent materials and realize the joint utilization of linear excitons and triplet excitons.Therefore,the maximum internal quantum efficiency of 100%can be realized in theory;The third generation of thermally activated delayed fluorescent material,which has a small singlet triplet energy level difference(△E_ST),can realize the return of triplet exciton to singlet state after reverse inter system jump（RISC）,which can greatly improve the utilization of triplet exciton,and the theoretical maximum internal quantum efficiency of the device can also reach 100%.It is worth noting that the internal mechanism of thermally activated delayed fluorescent materials is still not very clear,and some commercial indicators can not be met at the same time.Therefore,phosphorescent materials are still the materials with the best commercial prospect at present.Generally,materials used for luminescence need to be doped into certain subject materials to avoid luminescence quenching effect due to aggregation.Therefore,high-performance host materials are particularly important for OLED devices.The research direction of this thesis is the development of high-performance host materials.Our work is carried out from the following two parts:1.In the second chapter,we designed and synthesized a kind of fluorene as the core and designed four molecules（1TRz3Cz,1TRz3TPA,1Cz3TRz and 1TPA3TRz）through their C1-and C3-positions with different connection strategies.We studied the effects of different connection strategies by studying their thermochemical,photophysical and electrochemical properties,We obtained that the electron donating ability of the donor unit has an effect on the fluorescence emission peak,UV-Vis spectrum,singlet,triplet energy level and Homo value of the material.In addition,we can also find that the electronic interaction between 1-D and 3-A is more effective than that between 1-A and 3-D.The triplet energy level of 1TRz3Cz is 2.68 e V,which has a certain application prospect.2.In Chapter 2,we designed and synthesized a kind of fluorene as the core,and designed four molecules（2TRz3Cz,2TRz3TPA,2Cz3TRz and 2TPA3TRz）through their C2-and C3-positions with different connection strategies.By studying their thermochemical properties,photophysical properties and electrochemical properties,we studied the effects of different connection strategies,and analyzed their properties,We have obtained that the electron donating ability of donor elements has an impact on the fluorescence spectrum emission peak,UV-Vis spectrum,singlet,triplet energy level and Homo value of the material.We can also find that the electron interaction between 2-D and 3-A is more effective than that between 2-A and 3-D,which will affect the singlet,triplet energy level and Homo value of the material. Subsequently,we applied this type of fluorene materials to the main materials of PHOLED for the first time and made corresponding devices.The unusual 2,3-disubstituted fluorene can be regarded as a detuning connection strategy,which creates a distorted molecular conformation.This distorted three-dimensional spatial structure gives them good thermal properties and high et value.The devices prepared by 2TRz3TPA,2TRz3Cz,2TPA3TRz and2Cz3TRz have green phosphorescence,and all show good efficiency and smooth efficiency roll off.The device prepared by 2TRz3TPA has the highest power efficiency,and its PE value has exceeded 106 lm W^-1.In addition,G2 and G3 also have high power efficiency,both exceeding 100 lm W^-1.These results further expand the possibility of Fluorene Derivatives Used in efficient OLED materials.