Design,Synthesis And Application Of Thermally Activated Delayed Fluorescence Molecules Based On π-stacked Structure

Organic light-emitting diodes(OLEDs)have rapidly developed over the last three decades as a new generation of display and lighting technology.This is due to the collaborative efforts of various disciplines,including organic optoelectronic materials,semiconductor device physics,and computational science.Light-emitting materials have a direct impact on the characteristics of OLED devices,and extensive research has been conducted to meet market demands for high efficiency,full-color,high color purity,and high stability.This has led to the development of three generations of OLED emitters:fluorescent molecules,phosphorescent molecules,and thermally activated delayed fluorescence(TADF)molecules.TADF materials have gained popularity due to their competitive exciton utilization and lack of precious metals,and there are already TADF materials that meet various needs.However,efficient and stable blue emitters are relatively limited among red,green,and blue emitters,as their wide light-emitting band gap is not conducive to charge injection in devices.To address this issue,this thesis focuses on TADF molecules with a π-stacked structure and designs and synthesizes three pairs of blue emitters using weak electric group perturbation strategy and strong electric group significant modulation strategy.The photoelectric properties of these molecules are also explored.In Chapter 2,a multi-donor strategy was utilized to synthesize blue TADF emitters,namely 3TBO and 5TBO,by linking three 3,6-di-tert-butyl-9H-carbazole(tCz)units using a rigid planar oxygen-bridged boron-based(BO)fragment.The experiment results show that there is a π-stacked steric hindrance between the tCz donors,and the intramolecular charge transfer is mainly carried out by through bond charge transfer(TBCT).The steric hindrance also effectively prevented aggregation-induced quenching of BO acceptor fragments,thereby resulting in a significant enhancement of the photoluminescence quantum yield(PLQY)of 3TBO and 5TBO to 78.4%and 96.7%,respectively.Both 3TBO-and 5TBO-based OLED devices exhibit sky blue light emission at 484 nm and external quantum efficiency(EQE)of 17.3%and 26.2%,respectively.The primary focus of this work was the design and synthesis of multi-donor TADF molecules with π-stacked structures based on ortho-benzene.In Chapter 3,a methyl fine-tuning strategy was employed to introduce methyl groups into TADF molecules with π-stacked structures based on spirofluorene to synthesize the azure emitters,1MeDMB and 2MeDMB.The presence of the spirofluorene base can interrupt the conjugation of donor and acceptor fragments through valence bonding,resulting in both 1MeDMB and 2MeDMB exhibiting through space charge transfer(TSCT)properties.The incorporation of methyl groups mainly impacts the non-radiative transition rate.Moreover,X-ray diffraction analysis revealed a notable disparity in the stacking pattern between 1MeDMB and 2MeDMB.Ultimately,the doped film of 1MeDMB exhibited a higher PLQY than that of 2MeDMB.Both 1MeDMB and 2MeDMB were utilized to develop OLED devices with 492 mm and 496 nm emission and 28.8%and 23.3%EQE,respectively.The primary objective of this study was to investigate the role of methyl groups in TSCT TADF molecules.In Chapter 4.the 2,4,6-triphenyl-1,3,5-triazine fragment or BO fragment were incorporated into the C1 position of spirofluorene,and 5,12-diphenyl-5,12dihydroindolo[3,2-a]carbazole donor with a suitable triplet state energy level was positioned at the C9 position to synthesize the deep blue TADF emitters,ICZFTRZ and ICZFBO,respectively.Through quantum chemistry calculations and photophysical analyses,it was demonstrated that the donors and acceptors of ICZFTRZ and ICZFBO exhibit both π-stacked steric hindrance and TSCT interactions.The PLQYs of ICZFTRZ and ICZFBO were found to be 96.2%and 91.2%,respectively.The OLED devices based on ICZFTRZ and ICZFBO achieved blue emission at 472 nm and deep blue emission at 448 nm,respectively,with CIE(Commission International de l’Eclairage)coordinates of(0.155,0.221)and(0.150,0.072)and EQE of 18.4%and 12.2%,respectively.The primary focus of this investigation was on the design and synthesis of deep blue TSCT TADF molecules.