Theoretical Study Of Thermally Activated Delayed Fluorescent Materials Based On Benzophenone

OLED has extremely broad application prospects in the field of display and lighting.Compared with traditional LCD,OLED has better display effect and lower power consumption,the production process of OLED is greatly simplified and the cost is reduced.In addition,it can be used to produce display devices on flexible substrate,which is also of great application value in the field of wearable devices.Due to the 100% theoretical internal quantum efficiency of TADF,it is possible to replace traditional fluorescent and phosphorescent materials as the third generation of organic lightemitting materials.One of the main reasons for limiting the commercialization of TADF materials is its serious efficiency roll-off problem,and the introduction of aggregationinduced emission feature is expected to solve this problem.However,the mechanism of TADF has not been fully clarified at present,and the research on the mechanism of the efficiency roll-off is still not not detailed enough.The introduction of benzophenone receptor can make TADF material exhibit aggregation-induced luminescence effect and greatly improve the quantum efficiency of undoped devices.By designing and studying the molecules 2SPAc-BP,2NSPAc-BP and NSPAc-BP-SPAc,it was found that due to the strong charge transfer characteristics of the molecule and the large energy level difference between the singlet energy levels,the singlet exciton radiation transition is hindered.There is a strong coupling interaction between singlet orbits and triplet orbits,so singlet excitons at high energy levels can frequently switch between singlet and triplet states through intersystem crossing.The way will lead to hoarding and energy loss of excitons,and exacerbates the roll-off of device efficiency.In addition,through the theoretical research on the molecules DMF-BP-DMAC,CBM-DMAC,DCPDAPM,DBT-BZ-DMAC,DPF-BP-DMAC,CP-BP-DMAC and DMAC-BP,the parameter X is introduced to summarize the effects of the excited state properties and energy level differences of S1,T1 and T2 on the material performance,it is found that the parameter X with the reverse intersystem crossing(RISC)rate constant and the quantum efficiency of the device is roughly positively related.The Y parameter is introduced to measure the strength of the coupling interaction between the singlet orbitals and the triplet orbitals.The coupling interaction between the S1,T1 and T2 orbits will improve the quantum efficiency of the device,while the coupling interaction between the higher level orbits will reduce the quantum efficiency of the device and aggravate the device’s efficiency roll-off.In summary,the parameters X and Y can be used to predict the performance of TADF organic small molecules.