【作者】 陈杰；

【导师】 陈润锋； 陶冶；

【作者基本信息】 南京邮电大学 ， 电子信息（专业学位）， 2024， 硕士

【摘要】 具有热活化延迟荧光（TADF）性质的纯有机材料极大地提高了有机发光二极管（OLED）的效率,因为它们能够通过有效的反向系间窜越过程充分地利用三重态激子,这通常是在具有电荷转移性质的分子中实现的。迄今为止,除了常见的通过共价键电荷转移（TBCT）型TADF分子外,通过空间电荷转移（TSCT）型TADF分子由于固有的分子设计特性使其在单个分子中可以保持给体和受体单元良好的空间分离,能够有效减小前线轨道电子云的重叠,有利于实现极小的（35）E_ST,引起了研究者们广泛的兴趣。但是目前仍然存在一些挑战,例如TSCT型TADF分子存在构筑单元种类较少、发光量子产率较低、反向系间窜越速率较小、难以实现长波长发光等问题。本文围绕目前TSCT型TADF材料所存在的不足,通过从改变给/受体的空间排列、协同分子的TSCT/TBCT性质以及调节受体的吸电子能力这三个方面设计合成了一系列TSCT型TADF分子,研究内容如下:（1）针对于TSCT型TADF分子体系构筑单元种类稀缺的问题,提出了一种基于硫杂蒽的“U型”D-A排列策略,构建了两种新颖的TSCT型TADF小分子AC-TRZ与Cz-TRZ,进一步丰富和拓展了TSCT型TADF的小分子体系。通过空间限制电荷转移策略,给体与受体单元之间形成了良好的物理分离,并展现出面对面的排列构型,设计的分子表现出较小的（35）E_ST,分别为0.16和0.15 eV。基于AC-TRZ的OLED器件的启亮电压为3.17 V,最大的电流效率为17.3 cd A^-1,最大功率效率为16.3 lm W^-1,最大的外量子效率（EQE）为7.1%。为新型空间电荷转移型TADF材料的设计提供了一种可行的方案。（2）由于TSCT型TADF分子体系前线轨道重叠较小,导致了其辐射衰减速率较慢(10⁵-10⁶ s^-1),并且因为给/受体间的电子耦合作用较弱,使得其反向系间窜越速率较慢(～10⁵ s^-1)。提出了“协同TSCT与TBCT”与“准等效”给体的策略,通过在连接基团苯环上分别进行对、间、邻位取代成功设计合成了三种兼具TSCT和TBCT性质的TADF分子p-DPhCzTRZ、m-DPhCzTRZ和o-DPhCzTRZ。“准等效”的给体的设计构建了简并的激发态能级,促进了多种激发态的混合,打开了更多的反向系间窜越通道,最大的反向系间窜越速率接近10⁶数量级。同时由于TBCT的协同作用提高了前线轨道在苯环上的重叠,增强了振子强度,最大的辐射跃迁速率接近10⁷数量级。这为设计高反向系间窜越速率和高辐射跃迁速率的TSCT-TADF材料提供了一种新思路。（3）由于TSCT型TADF分子体系使用了非共轭连接结构且空间电荷转移相对较弱,导致了其发光大多局限在蓝绿光,难以实现长波长发光。提出了一种TSCT-TADF受体增强的策略,设计合成了一种以邻苯二甲酰胺作为受体的TSCT-TADF分子,邻苯二甲酰胺作为受体单元具有很强的吸电子能力,有效地降低了分子的最低空置分子轨道（LUMO）能级,能够显著地减小分子的光学能隙,从而实现了TSCT-TADF分子的较长波长的发光。得益于PhCzPI较大的斯托克斯位移和较小的（35）E_ST,将PhCzPI掺入聚砜（PSF）中制备成薄膜,并测试了其作为闪烁体材料的性能。结果表明,PhCzPI具有良好的辐射发光性能,其辐射发光强度达到了10⁴数量级(210 mGys^-1的辐射剂量率下),且对于X射线具有良好的响应性以及稳定性,为设计长波长发光的TSCT-TADF闪烁体提供了一种新思路。更多还原

【Abstract】 Pure organic materials with thermally activated delayed fluorescence（TADF）properties greatly improve the efficiency of organic light-emitting diodes（OLEDs）,as they can fully utilize triplet excitons through effective reverse intersystem crossing processes,which are typically achieved in molecules with charge transfer properties.So far,in addition to the common through covalent charge transfer（TBCT）TADF molecules,through space charge transfer（TSCT）TADF molecules have attracted widespread interest from researchers due to their ability to achieve extremely small single/triplet energy gaps(（35）E_ST).Due to its inherent molecular design characteristics,TSCT-TADF molecules can maintain good spatial separation between donor and acceptor units within a single molecule,effectively reducing the overlap of frontier orbital electron clouds and facilitating the achievement of very small（35）E_ST.However,there are still some challenges at present,such as the limited types of building units,low quantum yield of luminescence,low reverse intersystem transition rate,and difficulty in achieving long wavelength luminescence in TSCT-TADF molecules.This article focuses on the shortcomings of current TSCT-TADF materials,and designs and synthesizes a series of TSCT-TADF molecules by changing the spatial arrangement of donors and acceptors,the TSCT and TBCT properties of synergistic molecules,and regulating the electron absorption ability of acceptors.The research content is as follows（1）To solve the problem of the scarcity of building blocks of TSCT-TADF molecular system,two novel TSCT-TADF small molecules AC-TRZ and Cz-TRZ were constructed using rigid thiopanthracene structure as molecular scaffolds,which further enriched and expanded the small molecule system of TSCT-TADF.A good physical separation between the donor and acceptor units is achieved through a spatially limited charge transfer strategy,and the molecules designed based on this"U-shaped"D-A arrangement exhibit smaller（35）E_ST of 0.16 eV and 0.15 eV,respectively.The OLED device based on AC-TRZ has a lighting voltage of 3.17 V,a maximum current efficiency of17.3 CD A^-1,a maximum power efficiency of 16.3 lm W^-1,and a maximum external quantum efficiency（EQE）of 7.1%.It provides a new idea for the design of TADF molecules with space charge transfer.（2）The TSCT-TADF molecular system has a low radiative decay rate(10⁵-10⁶ s^-1)due to the small overlap of the front orbitals,and a low inverse intersystem crossover rate(～10⁵ s^-1)due to the weak electron coupling between donor and acceptor.Three TADF molecules,p-DPhCzTRZ,m-DPhCzTRZ and o-DPhCzTRZ,with the properties of TSCT and TBCT,were successfully designed and synthesized by performing para,meta,and ortho substitutions on the benzene of the connecting group respectively.The design of the"quasi-equivalent"donor builds degenerate excited state levels,promotes the mixing of multiple excited states,and provides more reverse intersystem channeling,with the maximum reverse intersystem channeling rate approaching 10⁶ orders of magnitude.At the same time,the introduction of TBCT improves the overlap of the front orbit on the benzene ring,enhances the vibrator intensity,and the maximum radiation transition rate is close to 10⁷ orders of magnitude.This provides a new strategy for the design of TSCT-TADF molecules with high reverse intersystem channeling rate and high radiative transition rate.（3）The TSCT-TADF molecular system utilizes a non-conjugated connection structure,resulting in relatively weak space charge transfer and limited luminescence to blue and green light.Achieving long wavelength luminescence has been challenging.However,as an acceptor unit,phthalamide possesses strong electron withdrawing ability,effectively reducing the LUMO energy level of the molecule and narrowing the optical energy gap to enable longer wavelength luminescence of TSCT-TADF molecules.The radioluminescent performance of PhCzPI was evaluated in polysulfone（PSF）films,demonstrating excellent intensity reaching 10⁴ orders of magnitude at a radiation dose rate of 210 mGys^-1.Furthermore,it exhibited good response and stability to X-rays,providing new insights for designing long wavelength luminescent TSCT-TADF scintillators.更多还原