Synthesis And Characterization Of Thermally Activated Delayed Fluorescent Material Based On Benzophenone

Thermally Activated Dalayed Fluorescence(TADF)as the third generation of organic electroluminescent materials for organic light-emitting diodes are attracting more and more attention.The traditional fluorescent materials have the disadvantage of low exciton utilization.While the phosphorescent materials use noble metals in order to achieve higher exciton utilization,which limites the development of the phosphorescent OLED materials.Comparinng with the first generationation of traditional fluorescent materials and the second generation of phosphorescent OLED materials,TADF materials have obvious advantages.Without using precious metals,the TADF material can utilize the thermal energy of its own molecule or the environment,which can achieve an reverse inter-system crossing(RISC)process from triplet(T1)to singlet(S1).This process enhances the delayed fluorescence.The triplet exciton can be completely converted into singlet state exciton when the energy level between the triplet exciton and the singlet exciton is small and the KRISC is large.Then the exciton utilization can reach theoretical limit that is 100%.Most of fluorescent materials exist in solid(such as solid film),the aggregation of fluorescent molecules are unavoidable.This problem limits the performance and application prospect of the organic electroluminescent devices.However,the appearance of aggregation-induced luminescence(AIE)molecule solves the above problems.The AIE molecules have weak luminescence in solution but strong emission in aggregation state.The discovery of AIE molecule greatly promotes the high efficiency of solid state application and the development of luminescent materials in organic electroluminescence.Combined with the characteristics of AIE and TADF,organic electroluminescent materials have both AIE and TADF properties.They can simultaneously solve the problems of high quenching and low exciton utilization of traditional fluorescent materials,and improve the device efficiency of the OLED effectively.This article did the following research:1.Designed and synthesized two thermally activated delayed fluorescent molecules DBT-BZ-Cz and DFT-BZ-Cz based on benzophenone and carbazole.Through systematic studies they have similar thermodynamic,electrochemical and photophysical properties.These two compounds as delayed fluorescent blue light emittering material(?PL=472 nm,470 nm respectively),and they have good thermodynamic stability(Td=339?,329?).The nondoped device based on DBT-BZ-Cz,the maximum luminescence brightness is 2349 cd/m2,the maximum current and power efficiency are 0.96 cd/A and 0.79 lm/W,respectively,and the maximum external quantum efficiency is 0.64 %.The doped device based on DBT-BZ-Cz.The maximum luminescence brightness is 2560 cd/m2,the maximum current and power efficiency are 3.46 cd/A and 2.58 lm/W,respectively.The maximum external quantum efficiency is 2.31 %.2.We designed and synthesized two aggregation-inducing delayed-fluorescence molecules 2DBT-BZ-2Cz and 2DFT-BZ-2Cz based on benzophenone and enoxazole.At the same time,they have good thermodynamic stability(Td =536 ?,525 ?).The nondoped device based on 2DBT-BZ-2Cz.The maximum luminance is 3923 cd/m2,the maximum current efficiency is 2.50 cd/A,the maximum power efficiency is 1.78 lm/W,the maximum external quantum efficiency is 0.91 %,and the CIE is(0.32,0.41).