Synthesis And Photoelectric Properties Of TADF Materials Based On Imide And Benzoyl Groups

TADF(Thermally Activated Delayed Fluorescence)materials are use pure organic molecules,The distribution of HOMO and LUMO on the donor/acceptor is regulated by the specific connection between donor and acceptor,overlap degree of frontier orbitals is reduced,which is beneficial to reduce?E_ST,and promote triplet exciton Reverse Intersystem Crossing process(RISC),which make the luminescence efficiency close to the level of the previous generation phosphorescent materials.It is of great significance to develop new and efficiency TADF materials to promote the development of OLED.The acceptor imide(Al)and benzoyl group have excellent photoelectric properties,in this paper,them were used in the following work:(1)Five kinds of materials,Al-4Cz?Al-4t Cz?Al-2t Cz?Al-3Cz and Al-9Cz,were synthesized by linking carbazole derivatives with different electron donating ability.Five materials exhibit blue to yellow green emission in solution,the emission wavelength of Al-4Cz is 460 nm,Al-4t Cz and Al-2t Cz are red shifted to 482 nm and495 nm by introducing tert-butyl,and conjugation degree of Al-3Cz and Al-9Cz is increased by introducing benzene ring,and their emission wavelength red-shifted to yellow green region(532 nm and 526 nm).The photoluminescence quantum yield(PLQY)of the five materials in the doped films is more than 20%,and the PQLY of Al-9Cz is the highest(40.0%).Several materials are doped into m CP host in OLED devices,the EL spectra of the devices doped with several materials are in the blue region of 450nm?485 nm.The EQE_maxof Al-2t Cz?Al-4t Cz?Al-3Cz and Al-9Cz devices are 1.12%?0.72%?15.97%and 4.33%,respectively,it shows that different connection modes of carbazole significantly affect the performance of the devices.Al-3Cz doped devices show the most excellent performance with L_max?CE_maxand PE_max of 2196 cd/m²?28.78cd/A and 2583 lm/W,indicate it has potential application in OLED.(2)The distorted structure of acceptor benzoyl group and donor phenoxazine was used as the skeleton,TP-BP and OTP-BP were synthesized by combining different triptycene derivatives.Both TP-BP and OTP-BP show aggregation induced luminescence(AIE),and the AIE enhancement of TP-BP is more obvious.The PLQY of TP-BP and OTP-BP doped in PMMA films reach 78.0%and 62.4%,respectively,indicates introduction of alkyl group increase of the group non radiative vibration.The doped and non-doped devices of TP-BP and OTP-BP are fabricated.Their EL spectra are in the yellow region(540 nm-560 nm).The performance of TP-BP devices is better than OTP-BP.The L_max,CE_max and EQE_max of the non-doped devices are 44010 cd/m²,41.04 cd/A,13.4%,respectively,and the device efficiency roll down is hardly zero.This indicates that the triptycene structure without alkyl groups can better inhibit the intermolecular stacking and improve the device performance of the materials.(3)PER-BP and TBP-BP materials were synthesized by planar polycyclic aromatic hydrocarbons(perylene and terphenylene)combine with the benzoyl group and phenoxazine structure.Two materials different aggregation forms lead to emission changes in the different concentrations,its emission wavelengths were different in the1%PMMA and solid.PER-BP and TBP-BP both have AIE properties in mixed solution of THF/H₂O,they PLQY of doped films is 31.1%and 75.8%,respectively.The lower PLQY of PER-BP is due to the strong aggregation-inducing quenching property of the perylene group itself.Electroluminescent devices were fabricated with PER-BP and TPE-BP.TPE-BP showed significantly better performance.The L_max,CE_max and EQE_max of the non-doped device were 18840 cd/m²?16.80 cd/A?6.3%,respectively,and the efficiency Roll-off was less than 3%at L=1000 cd/m².It shows that the combination of TPE-BP skeleton has better AIE and device performance.