Research Of Thermally Activated Delayed Fluorescent Organic Electroluminescent Materials Based On Indolocarbazole

Compared with other traditional inorganic light-emitting devices,the organic light-emitting diodes(OLED)have more advantages and enough potential to be used in display and lighting fields.After decades of research,the third-generation organic light-emitting materials,thermally activated delayed fluorescence(TADF)materials,were found out and have been one of the focuses of OLEDs research due to its high efficiency,environmental protection,and convenient preparation.Based on the reasonable molecular design strategy,the first excited singlet state(S₁)and the first excited triplet state(T₁)of TADF molecules can be effectively adjusted,which can reduce the electron exchange energy(?E_ST)of the molecule.Benefit from this,seventy-five percent of the T₁ state excitons produced by electrical excitation can be upconverted to S₁ state excitons using ambient heat,achieving 100%internal quantum efficiency.Usually,in order to get a small electron exchange energy,the TADF molecule is designed using a strategy,which need to connect the donor and acceptor through a conjugation structure.Compared with the abundant acceptors,there are fewer choices for donors.To slove this problem,we selected indole[3,2-b]carbazole as the donor core,designed and synthesized three new TADF molecules in this paper.The results are as follows:1.A new sky blue TADF material m BP-ICz selecting indolo[3,2-b]carbazole as the donor core and benzophenone connected to the meta position as the acceptor was designed.Compared to the literature,this article changed the connection site between the donor and acceptor,which increases the torsion angle.So the highest occupied orbital(HOMO)and the lowest unoccupied orbital(LUMO)are further separated,achieving a 0.03 e V electronic exchange energy.The color coordinate of organic light-emitting diodes based on m BP-ICz was(0.20,0.42).The maximum brightness of the device was 33600 cd/m²,and the external quantum efficiency could reach 17.2%.These results indicate that the material m BP-ICz,based on the indolo[3,2-b]carbazole donor,is a raw TADF molecule.The indolo[3,2-b]carbazole is an excellent donor,which can be used in the design of TADF materials.2.In order to improve the device efficiency,two new kinds of TADF materials,p TRZ-ICz and m TRZ-ICz,were designed and synthesized through changing the connection site between the donor and aceptor.Indolo[3,2-b]carbazole was used as the donor,while 2,4,6-triphenyltriazine was used as the acceptor.Judging from the structure of the two TADF molecules,they have a large dihedral angle for the plane between donor and acceptor,which could promote the separation of HOMO and LUMO and reduce the electron exchange energy of the materials.The electron exchange energies of the two materials were 0.05 e V and 0.13 e V,respectively,which indicate their potential TADF characteristic.The color coordinates of the devices based on pTRZ-ICz and mTRZ-ICz were(0.19,0.38)and(0.23,0.41),respectively,showing a sky blue emission.The maximum brightness of the device could reach 16440 cd/m² and 9770 cd/m²,and the maximum external quantum efficiency can reach 23.1% and 16.2%.These results indicate that indolo[3,2-b]carbazole is suitable for the design and synthesis of TADF molecules.