EQEmax of 21.0%, with a suppressed efficiency roll-off. The characterization of related photophysical properties revealed that embedding various boron, nitrogen, oxygen, and sulfur heteroatoms in the fused polycyclic π-system can finely regulate the narrowband pure-blue and deep-blue emissions of the emitters, and achieved efficient RISC processes.39 Consequently, OLEDs based on BOBS-Z, and BSBS-Z demonstrated narrowband and ultrapure-blue EL emissions, peaking at 456/463 nm and FWHMs of 22/23 nm, leading to CIEy coordinates of 0.06/0.08. Particularly, the EQEmaxs of two OLEDs reached 26.9% and 26.8%, respectively, and small efficiency roll-offs at a practical luminance were achieved.
EQE最大值为 21.0%,效率滚降受到抑制。相关光物理性质的表征表明,在稠合多环π体系中嵌入各种硼、氮、氧和硫杂原子可以精细调控发射器的窄带纯蓝色和深蓝色发射,并实现高效的RISC过程。 39因此,基于BOBS-Z和BSBS-Z的 OLED表现出窄带和超纯蓝色 EL 发射,峰值为 456 463 nm,半高宽为 22 23 nm,导致CIE y坐标为 0.06 0.08。特别是,两种OLED的EQE max s分别达到26.9%和26.8%,并且在实际亮度下实现了较小的效率滚降。
In 2022, our group developed two ternary N/B/S-based polycyclic heteroaromatic emitters (SBSN and DBSN) from bluish-green (489 nm) to yellow (553 nm) via tuning the coordination between B/N and S atom, aiming to increase CT delocalization of the emitters and improve photophysical properties.40 This strategy endows the two emitters with small FWHMs of 27 and 28 nm, respectively. Additionally, considerable kRISC values were achieved owing to the small ∆EST values of 0.10 - 0.13 eV and large SOC values. Consequently, the OLEDs emitting bluish-green and yellow emissions based on these two emitters showed the EQEmaxs of 17.6% and 21.8%, respectively, with low efficiency roll-offs. Subsequently, by the ternary combination of para-arrayed B-π-B, N-π-N, and S-π-S, Wang et. al. developed two red narrowband emitters, DBNS and DBNS-tBu,41 whose emissions peaking at 631 and 641 nm with FWHMs of 40 and 39 nm in toluene. Benefiting from the heavy-atom effect of S atom, high kRISC values of 2.1 × 105 s-1 and 2.2 × 105 s-1 and short τds of 11.2 and 10.2 μs were obtained. These results indicated that introducing S atoms into the resonance skeleton can effectively improve the SOC values and kRISC for MR-TADF emitters, thereby achieving efficient OLEDs with low efficiency roll-offs
2022年,我们课题组通过调节B/N和S原子之间的配位,开发了两种基于三元N/B/S的多环杂芳族发射体(SBSN和DBSN),从蓝绿色(489 nm)到黄色(553 nm)增加发射器的 CT 离域并改善光物理性质。40 这种策略使两个发射器分别具有 27 和 28 nm 的小 FWHM。此外,由于 0.10 - 0.13 eV 的小 ΔEST 值和大的 SOC 值,获得了相当大的 kRISC 值。因此,基于这两种发射器发出蓝绿光和黄光的 OLED 的 EQEmax 分别为 17.6% 和 21.8%,效率滚降较低。随后,Wang等人通过对位排列的B-π-B、N-π-N和S-π-S的三元组合。等人。开发了两种红色窄带发射器 DBNS 和 DBNS-Bu41,其在甲苯中的发射峰值为 631 和 641 nm,半高宽为 40 和 39 nm。受益于S原子的重原子效应,获得了2.1×105 s-1和2.2×105 s-1的高kRISC值以及11.2和10.2 μs的短τds。这些结果表明,将S原子引入到共振骨架中可以有效提高MR-TADF发射器的SOC值和kRISC,从而实现具有低效率滚降的高效OLED.
2.1.2 Selenium-containing MR-TADF emitters
2.1.2 含硒MR -TADF发射体
Considering the main group effect, Se atom has a stronger heavy atom effect compared to the S atom, so organic integration of Se and MR-TADF materials may endows it with a more efficient RISC processes (Figure 3). Yasuda et. al. firstly doped Se atom into a MR-TADF emitter (CzBSe),37 yielding a record kRISC exceeding 108 s-1, which is three orders of magnitude higher than that of common MR-TADF emitters. The theoretical calculations indicated that CzBSe possesses a quite large SOC (5 cm-1 for <S1|ĤSOC|T2> and 10 cm-1 for <S1|ĤSOC|T3>) value, which higher than that of CzBS and CzBO. Benefitting from an ultrafast triplet-exciton up-conversion of CzBSe, corresponding OLED offered an EQEmax of 23.9%, with a narrow blue emission (λEL = 481 nm, FWHM = 33 nm) and a significantly alleviated efficiency roll-off. Based on this framework, Wang et al introduced additional tert-butyl and peripheral 3,6-di-tert-butylcarbazole moieties to two Se-integrated MR-TADF emitters, Cz-BSeN and DCz-BSeN.42 Cz-BSeN and DCz-BSeN showed sky-blue emissions peaking at 479 and 472 nm with FWHMs of 30 and 28 nm, respectively. Notably, these two emitters showed large SOC values (2.51 and 3.96 cm-1) and high kRISC of 7.5 × 106 and 8.8 × 106 s-1 for Cz-BSeN and DCz-BSeN, respectively. The OLEDs based on Cz-BSeN and DCz-BSeN displayed narrowband EL emissions with peaks at 490 and 481 nm, as well as small FWHMs of 36 and 32 nm, accompanied by EQEmaxs of 20.3% and 22.3%, respectively. Impressively, these two OLEDs achieved suppressed efficiency roll-offs with EQE values of 16.9%/19.6% at 100 cd m-2 and 13.7%/15.6% at 500 cd m-2, respectively. This work revealed the N/B/Se-based MR-TADF molecules for the development of highly efficient narrowband blue OLEDs with low-efficiency roll-offs
考虑到主族效应,Se原子比S原子具有更强的重原子效应,因此Se和MR-TADF材料的有机整合可能赋予其更高效的RISC工艺(图3)。安田等。等人。首先将 Se 原子掺杂到 MR-TADF 发射器 (CzBSe) 中,37 产生了超过 108 s-1 的创纪录的 kRISC,比常见的 MR-TADF 发射器高出三个数量级。理论计算表明CzBSe具有相当大的SOC(5 cm-1和 10 cm-1 为)值,高于CzBS和CzBO。受益于 CzBSe 的超快三线态激子上转换,相应的 OLED 的 EQEmax 为 23.9%,具有窄蓝色发射(λEL = 481 nm,FWHM = 33 nm),并且效率滚降显着减轻。基于该框架,Wang等人向两个Se集成的MR-TADF发射体Cz-BSeN和DCz-BSeN42Cz-BSeN和DCz-BSeN引入了额外的叔丁基和外围3,6-二叔丁基咔唑部分。 -蓝色发射峰值在 479 和 472 nm,半高宽分别为 30 和 28 nm。值得注意的是,这两个发射器表现出较大的 SOC 值(2.51 和 3.96 cm-1),Cz-BSeN 和 DCz-BSeN 的 kRISC 分别为 7.5 × 106 和 8.8 × 106 s-1。基于Cz-BSeN和DCz-BSeN的OLED显示出窄带EL发射,峰值为490和481 nm,以及36和32 nm的小FWHM,EQEmax分别为20.3%和22.3%。令人印象深刻的是,这两种 OLED 实现了抑制效率滚降,100 cd m-2 时的 EQE 值分别为 16.9%/19.6%,500 cd m-2 时的 EQE 值分别为 13.7%/15.6%。这项工作揭示了基于 N/B/Se 的 MR-TADF 分子,用于开发具有低效率滚降的高效窄带蓝色 OLED.
Furthermore, Yang et al reported a heavy Se atom incorporating emitter, BNSeSe,43 showing a PLQY~100% and the kRISC of 2.0 × 106 s-1, which is prior to most MR-TADF materials. The corresponding OLED exhibited an excellent EQEmax of 36.8% with a low efficiency roll-off (efficiency roll-off values of 2.8% and 14.9% at 1000 cd m-2 and 10000 cd m-2, respectively). Besides, BNSeSe was firstly used as an assist dopant to sensitize the low-energy MR-TADF emitter (BN3),44 the hyperfluorescence OLED exhibited a significant EQEmax beyond 40% with a low efficiency roll-off. This work sheds a new light on MR-TADF emitters or sensitizers towards high-performance OLEDs. Later, Yang et. al. developed a green narrowband MR-TADF emitter, BN-STO,45 through peripherally introducing a Se-embedded selenoxanthone unit to a MR-TADF skeleton. BN-STO exhibited a green narrowband emission, peaking at 506 nm with a small FWHM of 29 nm. And a high kRISC value of 1.2 × 105 s-1 was achieved owing to the strong SOC caused by the peripheral Se atom integration. The BN-STO-based OLED showed a high EQEmax of 40.1% with a suppressed efficiency roll-off. These results demonstrate that the peripheral modification of heavy-atom and direct integration of heavy atom into the MR-TADF framework is helpful for improving RISC processes of MR-TADF emitters.
此外,Yang等人报道了结合发射极BNSeSe 43 的重Se原子,其PLQY ~100%和k RISC为2.0×10 6 s -1 ,这优于大多数MR-TADF材料。相应的OLED表现出优异的EQE max 36.8%和低效率滚降(在1000 cd m -2和10000 cd m -2时效率滚降值分别为2.8%和14.9%)。此外, BNSeSe首先被用作辅助掺杂剂来敏化低能 MR-TADF 发射体 ( BN3 ), 44超荧光OLED表现出超过 40%的显着 EQE 最大值,且效率滚降较低。这项工作为高性能 OLED 的 MR-TADF 发射器或敏化剂提供了新的思路。后来,杨等人。等人。通过在 MR-TADF 骨架外围引入 Se 嵌入的硒氧蒽酮单元,开发了一种绿色窄带 MR-TADF 发射器BN-STO 45 。 BN-STO表现出绿色窄带发射,峰值为 506 nm,半高宽为 29 nm。由于外围Se原子集成引起的强SOC,实现了1.2×10 5 s -1的高k RISC值。基于BN-STO的OLED表现出高达40.1% 的高EQE ,并且效率滚降受到抑制。这些结果表明,重原子的外围修饰以及重原子直接集成到MR-TADF框架中有助于改进MR-TADF发射器的RISC工艺。
Figure 3. Molecular structures of Se-containing MR-TADF emitters.
图3 .含硒 MR-TADF 发射体的分子结构。
2.2 Metal-perturbed MR-TADF materials
2.2 金属扰动MR- TADF材料
The aforementioned publications have shown that heavy atoms can enhance the SOC values of MR-TADF materials, thereby improving kRISC. In addition to the usual heavy atoms (S, Se), some metal atoms with high atomic numbers can also improve kRISC. Of course, the selection of metal ions requires careful consideration, otherwise the strong SOC effect will cause molecules to exhibit phosphorescence rather than TADF. Considering the actual difficulty of synthesis and the selectivity of metal ions with weak SOC, there are only a few successful examples have been reported regarding metal perturbations, such as gold (Au(I)) and Pt(II) (Figure 4). By introducing metal centers to fundamentally modify the excited state dynamics, a feasible solution for improving MR-TADF emission without sacrificing color purity has been demonstrated. In 2022, Yang et al proposed a MR-TADF emitter, DCzBN-Au,46 through coordination of Au with a B/N-embedded polycyclic ligand. Due to the Au(I)-complex perturbation, the kRISC value was dramatically accelerated to 2.3 × 107 s-1, leading to a τd as short as 4.3 µs. Meanwhile, a PLQY of 95% and a FWHM of 39 nm were essentially unchanged after metal Au(I) coordination. Consequently, the OLED based on DCzBN-Au exhibited an EQEmax of 35.8% without TADF sensitization. And the EQE was still maintained as high as 32.3% at 10000 cd m-2. At the same time, Chi et al also developed a series of similar Au-based MR-TADF material, (BzIPr)AuBN, (PzIPr)AuBN and (PylPr)AuBN.47 All the MR-TADF emitters displayed green emissions with the maximum peaks at around 510 nm with small FWHMs as 30 nm. Benefiting from the influence of Au(I) coordination disturbance, the high rates kRISC ≈ 106 s-1 were afforded, which were significantly enlarged about two orders of magnitude compared to those metal-free B/N-based MR-TADF emitters, and consequently, their τds were notably reduced to 5.5-27.0 μs with a mono-exponential function. Consequently, the OLEDs utilizing these Au(I)-based MR-TADF emitters showed green narrowband EL emissions, peaking at 508-517 nm with narrow FWHMs of 34-40 nm. Notably, Au(I)-based OLEDs displayed high EQEs of up to 30.3% and suppressed efficiency roll-offs of 0.8%−6.0%, as well as a long operational lifetime (LT60) of 1210 h at 1000 cd m-2. These metal-perturbed MR-TADF molecular design can greatly promote T1 harvesting, thereby achieving high-performance MR-TADF-OLEDs and opening up a new dimension for the design of practical MR-TADF emitters.
上述出版物表明,重原子可以提高MR-TADF材料的SOC值,从而提高k RISC 。除了通常的重原子(S、Se)之外,一些原子序数较高的金属原子也可以提高k RISC 。当然,金属离子的选择需要仔细考虑,否则强SOC效应会导致分子表现出磷光而不是TADF。考虑到合成的实际难度以及弱SOC金属离子的选择性,成功的例子屈指可数。有关金属扰动的报道已有报道,例如金 (Au(I)) 和Pt( II) (图 4) 。通过引入金属中心从根本上改变激发态动力学,已经证明了一种在不牺牲色纯度的情况下改善 MR-TADF 发射的可行解决方案。 2022年,Yang等人通过Au与B/N嵌入的多环配体的配位提出了一种MR-TADF发射体DCzBN-Au 46 。 由于Au (I)复合物扰动, k RISC值急剧加速至2.3 × 10 7 s -1 ,导致τ d短至4.3 µs。同时,金属Au (I)配位后, PLQY为95%, FWHM为39 nm,基本没有变化。因此,基于DCzBN -Au的 OLED在没有 TADF 敏化的情况下表现出35.8% 的n EQE max 。并且在10000 cd m -2时EQE仍保持高达32.3% 。同时,Chi等人还开发了一系列类似的Au基MR-TADF材料, ( BzIPr ) AuBN ( PzIPr ) AuBN和( PylPr )AuBN 47所有MR-TADF发射器都显示出绿光发射,最大峰值为约 510 nm ,半高宽小为 30 nm。 受益于Au(I)配位扰动的影响,获得了高速率k RISC ≈ 10 6 s -1 ,与无金属B/N基MR-TADF发射器相比,显着提高了约两个数量级,因此它们的τ d s通过单指数函数显着降低至 5.5-27.0 μs 。因此,利用这些基于 Au (I)的 MR-TADF 发射器的 OLED显示出绿光窄带 EL 发射峰值为 508-517 nm,半峰宽为 34-40 nm。值得注意的是,基于Au (I)的OLED 表现出高达30.3% 的高 EQE,并抑制了0.8%−6 的效率滚降。0%,以及在1000 cd m -2下1210 h的长工作寿命(LT 60 )这些金属扰动的MR-TADF分子设计可以极大地促进T 1收集,从而实现高性能MR-TADF-OLED和为实用 MR-TADF 发射器的设计开辟了新的维度。
Figure 4. Molecular structures of metal-containing MR-TADF emitters.
图4 .含金属 MR-TADF 发射体的分子结构。
Recently, Liu et. al. designed and synthesized a Pt(II)-based MR-TADF emitter (BNCPPt) by integrating a reported MR-TADF unit into the classical heavy metal Pt(II) complex. As expected, BNCPPt exhibited larger <S1|ĤSOC|T1>s from S1→T1 and T1→S0 (<S1|ĤSOC|T1> = 2.82 cm-1, <T1|ĤSOC|S0> = 14.19 cm-1) due to the strong SOC effect induced by the Pt(II) participation. The solution-processed OLED employing BNCPPt displayed a green emission, peaking at 507 nm, with a narrow FWHM of 35 nm, and realized an EQEmax of 13.5% with a very low efficiency roll-off of 4.4% at 1000 cd m-2.48 This design concept provides an ingenious combination of multi-resonance motif and metal complex, proposing a novel strategy to construct MR-TADF emitters toward high-performance OLEDs.
最近,刘等人。等人。通过将报道的 MR-TADF 单元集成到经典的重金属Pt ( II)配合物中,设计并合成了Pt ( II)基 MR-TADF 发射器 ( BNCPPt ) 。正如预期的那样, BNCPPt从 S 1 → T 1和 T 1 → S 0表现出更大的 <S 1 Ĥ SOC | T 1 % 3E (<S 1 Ĥ SOC |T 1 > = 2.82 cm -1 , <T 1 Ĥ SOC |S 0 > = 14.19 cm -1 )由于强 SOC效应铂( II)参与。 采用BNCPPt的溶液处理 OLED显示出绿光发射,峰值为 507 nm,半峰宽为 35 nm,并实现了13.5%的n EQE max ,在 1000 cd m 时效率滚降为 4.4% 。 2 48这种设计理念提供了多共振基序和金属配合物的巧妙结合,提出了一种构建 MR-TADF 发射器的新策略高性能 OLED。
2.3 π-Conjugation extended MR-TADF emitters
2.3 π-共轭扩展MR- TADF发射器
In addition to enhance the SOC of MR-TADF emitters to promote the RISC process of T1 excitons, reducing ∆EST is also an effective strategy to improve kRISC (Figure 5). In 2019, Zysman-Colman and Olivier calculated and simulated a series of B/N based emitters. Impressively, as the conjugated backbones of the molecule extends, the intramolecular charge transfer delocalization becomes more pronounced. As a result, ∆EST will decrease and f OSC will increase.49 At the same time, Hatakeyama et. al. developed a narrowband deep-blue emitting MR-TADF material ν-DABNA, which consisting of five connected benzene rings, two boron and four nitrogen atoms, as well as two diphenylamino substituents.50 Compared to the DABNA-1 and DABNA-2, the CT delocalization of ν-DABNA is more pronounced, providing a smaller ∆EST of 0.017 eV and a larger kRISC of 2.0 × 105 s-1. The deep-blue OLED based on ν-DABNA showed an excellent EQEmax of 34.4%. Notably, the efficiency roll-off (1.6% and 8.6% at 100 and 1000 cd m-2, respectively) is smaller than most deep-blue OLEDs.
除了提高MR-TADF发射极的SOC来促进T 1激子的RISC过程外,降低Δ E ST也是提高k RISC的有效策略(图5 )。 2019 年,Zysman-Colman 和 Olivier 计算并模拟了一系列基于 B/N 的发射器。令人印象深刻的是,随着分子的共轭主链延伸,分子内电荷转移离域变得更加明显。结果,Δ E ST将减少, OSC将增加。 49同时,Hatakeyama等人。等人。开发了一种窄带深蓝色发射MR-TADF材料ν -DABNA ,它由五个相连的苯环、两个硼和四个氮原子以及两个二苯氨基取代基组成。 50与DABNA-1和DABNA-2相比, ν -DABNA的 CT 离域更加明显,提供更小的 Δ E ST为 0。017 eV 和更大的k RISC 2.0 × 10 5 s -1 。基于ν -DABNA的深蓝色OLED表现出优异的EQE最大值为34.4%。值得注意的是,效率滚降(在 100 cd m -2 和 1000 cd m -2下分别为 1.6% 和 8.6%)小于大多数深蓝色 OLED。
The π-conjugation extension of MR-TADF emitters is diverse. In 2019, Wang et al. constructed a bluish-green narrowband emitter, DtBuCzB, by replacing tert-butyl carbazole with diphenylamine.51 Furthermore, by expanding the π-conjugated skeleton of the parent bis(di[t-butyl]carbazol)phenylene, an efficient narrowband green emissive molecule, DtBuPhCzB, was successfully developed. DtBuPhCzB exhibited a smaller ∆EST and better TADF performances than that of DtBuCzB. Based on DtBuPhCzB dopant, a green narrowband OLED was prepared, with an EQEmax of 25.5% and a FWHM of 33 nm. In 2022, Wang et al. used DtCzB as a synthon and utilized the Scholl oxidative coupling reaction to construct a large π-conjugated MR-TADF material, BN-TP,52 which exhibited a vivid green emission, peaking at 523 nm, and a narrow FWHM of 34 nm. Benefitting from efficient exciton up-conversion from Tn state to S1 state, BN-TP exhibited good TADF performances with a kRISC of 104 orders of magnitude, and OLED based on BN-TP showed an ultrapure green emission with a peak of 528 nm, and CIE coordinates of (0.26, 0.70), as well as an EQEmax of 35.1%.
MR-TADF 发射体的 π 共轭延伸是多种多样的。 2019 年,王等人。通过用二苯胺取代叔丁基咔唑,构建了蓝绿色窄带发射器DtBuCzB 。 51此外,通过扩展母体双(二[ -丁基]咔唑)亚苯基的π-共轭骨架,成功开发了一种高效的窄带绿光发射分子DtBuPhCzB 。与DtBuCzB相比, DtBuPhCzB表现出更小的 Δ E ST和更好的 TADF性能。基于DtBuPhCzB掺杂剂,制备了绿色窄带OLED,其n EQE max为25.5%,半高宽为33 nm。 2022 年,Wang 等人。使用DtCzB作为合成子,并利用Scholl氧化偶联反应构建了大型π共轭MR-TADF材料BN-TP 52,该材料表现出鲜艳的绿光发射,峰值波长为523 nm,半高宽为34 nm。 受益于从T n态到S 1态的高效激子上转换, BN-TP表现出良好的TADF性能, k RISC达到10 4数量级,并且基于BN-TP的OLED表现出超纯绿光发射,峰值为 528 nm,CIE坐标为 (0.26, 0.70), n EQE最大值为 35.1%。
In 2019, Duan and co-workers successfully synthesized a novel hybridized MR-TADF material, AZA-BN,53 whose emission peaking at 522 nm with a FWHM of 28 nm in toluene solution. Due to the reasonable orbital hybridization and CT delocalization, AZA-BN exhibited a small ∆EST of 0.18 eV and a high PLQY of 94%. And the corresponding pure-green OLED displayed an EQEmax of 28.2% with a FWHM of merely 30 nm and a CIEy of 0.69. Furthermore, through the precise synthesis of multiple resonance fragments, the extended π-conjugation length, increased molecular rigidity, and reduced vibration frequency can be simultaneously reflected on BN-ICz molecule, which showing a pure green emission peaking at 521 nm and a PLQY of 99%. The OLED based on BN-ICz exhibited a record-high CIEy of 0.74 and an EQEmax of 30.5%.54
2019年,段和同事成功合成了一种新型杂化MR-TADF材料AZA-BN 5 3,其在甲苯溶液中的发射峰为522 nm,半高宽为28 nm。由于合理的轨道杂化和CT离域, AZA-BN表现出0.18 eV的小ΔE ST和高达94 %的PLQY 。相应的纯绿色 OLED 显示n EQE max为 28.2%,FWHM 仅 30 nm , CIE y为 0.69。此外,通过多个共振片段的精确合成,延长的π共轭长度、增加的分子刚性和降低的振动频率可以同时反映在BN - ICz分子上,在521 nm处呈现出纯绿光发射峰,PLQY为99%。基于BN- ICz的OLED表现出创纪录的0.74的CIE y和30.5%的n EQE max 。 5 4
Later, Yasuda group proposed two para B-π-N and B-π-B strategies to change donor and acceptor strengths, which aiming to adjust molecular ∆EST.55 And narrowband deep-blue and red emitters, BBCz-DB and BBCz-R, exhibited moderate kRISC values of 1.9 and 1.2 × 104 s-1, which are better than the parent molecule BBCz-SB. OLEDs based on BBCz-DB and BBCz-R displayed the EQEmax values of 29.3% and 22.0%, respectively.
随后,Yasuda课题组提出了两种para B - π - N和B - π - B策略来改变供体和受体强度,旨在调整分子 Δ E ST 5 5和窄带深蓝色和红色发射体, BBCz -DB和BBCz -R ,表现出中等的k RISC值,分别为 1.9 和 1.2 × 10 4 s -1 ,优于母体分子BBCz -SB 。基于BBCz -DB和BBCz-R的OLED显示EQE最大值分别为29.3 %和22.0 %。
In 2020, Hatakeyama et al reported a series of carbazole-based DABNA analogs (CzDABNAs)56 from triarylamine by regioselective one-shot single and double borylation. This facile and scalable synthesized strategy achieved the comprehensive construction of CzDABNAs by selectively boronation at the ortho-position of the carbazole group, exhibiting a narrowband emission. Similar to the results of previous calculated simulations by Oliver et al., the introduction of double borylation further increases the CT delocalization of molecules, while achieving smaller ∆EST and higher kRISC. For example, the ∆ESTs are 0.18 and 0.11 eV for single borylation CzDABNA-NP-M/TB and double borylation Cz2B2-M/TB, respectively, with kRISCs of 1.1 × 105 s-1 and 3.1 × 105 s-1, respectively. This work indicated that π-conjugation extension can effectively increase CT delocalization, thereby reducing ∆EST and accelerating kRISC. Later, Hatakeyama reported an ultra-pure blue MR-TADF material (ν-DABNA-O-Me)57 by oxygen atom incorporation. Because of restricted π-conjugation of the HOMO rather than the LUMO induced by oxygen atom incorporation, ν-DABNA-O-Me showed a hypsochromic shift compared to the parent ν-DABNA. And OLED based on ν-DABNA-O-Me exhibited an EL emission at 465 nm with a small FWHM of 23 nm and a high EQEmax of 29.5%. Recently, our group proposed two π-extended MR-TADF emitters, NBO and NBNP,58 whose emissions peaking at 487 and 500 nm by fusing conjugated high-triplet-energy units (carbazole, dibenzofuran)
2020年,Hatakeyama等人通过区域选择性单次和双硼化从三芳胺中报道了一系列基于咔唑的DABNA类似物(CzDABNAs)56。这种简便且可扩展的合成策略通过在咔唑基团的邻位选择性硼化实现了 CzDABNA 的全面构建,并表现出窄带发射。与 Oliver 等人之前计算模拟的结果类似,双硼化的引入进一步增加了分子的 CT 离域,同时实现更小的 ΔEST 和更高的 kRISC。例如,单硼化 CzDABNA-NP-M/TB 和双硼化 Cz2B2-M/TB 的 ΔEST 分别为 0.18 和 0.11 eV,kRISC 分别为 1.1 × 105 s-1 和 3.1 × 105 s-1 。这项工作表明π共轭延伸可以有效增加CT离域,从而减少ΔEST并加速kRISC。后来,Hatakeyama通过氧原子掺入报道了一种超纯蓝色MR-TADF材料(ν-DABNA-O-Me)57。由于氧原子掺入引起的HOMO而不是LUMO的受限π共轭,ν-DABNA-O-Me与母体ν-DABNA相比表现出低色位移。基于ν-DABNA-O-Me的OLED在465 nm处表现出EL发射,FWHM小为23 nm,EQEmax高达29.5%。最近,我们小组提出了两种π扩展的MR-TADF发射器,NBO和NBNP58,通过融合共轭高三线态能量单元(咔唑、二苯并呋喃),其发射峰值在487和500 nm