The development of efficient non‐doped organic light‐emitting diodes (OLEDs) is highly desired but very challenging because of a severe aggregation‐caused quenching effect. Herein, we present a heptagonal diimide acceptor (BPI), which can restrict excessive intramolecular rotation and inhibit close intermolecular π–π stacking due to well‐balanced rigidity and rotatability of heptagonal structure. The BPI‐based luminogen (DMAC‐BPI) shows significant aggregation‐induced delayed florescence with an extremely high photoluminescence quantum yield (95.8 %) of the neat film, and the corresponding non‐doped OLEDs exhibit outstanding electroluminescence performance with maximum external quantum efficiency as high as 24.7 % and remarkably low efficiency roll‐off as low as 1.0 % at 1000 cd m−2, which represents the state‐of‐the‐art performance for non‐doped OLEDs. In addition, the synthetic route to DMAC‐BPI is greatly streamlined and simplified through oxidative Ar−H/Ar−H homo‐coupling reaction.
Multi-resonance boron-nitrogen-containing thermally activated delayed fluorescence (MR-TADF) emitters have experienced great success in assembling narrowband organic light-emitting diodes (OLEDs). However, the slow reverse intersystem crossing rate (k RISC ) of MR-emitters (10 3 -10 5 s À 1 ) that will lead to severe device efficiency roll-off has received extensive attention and remains a challenging issue. Herein, we put forward a "space-confined donor-acceptor (SCDA)" strategy to accelerate RISC process. The introduction of SCDA units onto the MR-skeleton induces intermediate triplet states, which leads to a multichannel RISC process and thus increases k RISC . As illustrated examples, efficient MR-emitters have been developed with a submicrosecond delayed lifetime and a high k RISC of 2.13 × 10 6 s À 1 , which enables to assemble high-performance OLEDs with a maximum external quantum efficiency (EQE max ) as high as 32.5 % and an alleviated efficiency roll-off (EQE 1000 : 22.9 %).
The development of multiple heterohelicenes
with a high luminescence
dissymmetry factor (g
lum) is an appealing
yet challenging task. Herein, we disclose the synthesis of a structurally
unusual furan-based triple oxa[7]helicene, which represents the first
reported triple hetero[7]helicene, via [2+2+2] cyclotrimerization/intramolecular
dehydrogenative annulation. Compared to the reported double oxa[7]helicene,
the triple oxa[7]helicene exhibits an improved g
lum value of 1.8 × 10–3, exemplifying
the potential of the helicene subunit multiplication approach to enhance
the g
lum of heterohelicenes.
A highly efficient Rh(III)-catalyzed oxidative C−H/C−H cross-coupling of [1,2,4]triazolo[1,5-a]pyrimidines (TAP) with indoles and pyrroles has been developed, which provides an opportunity to rapidly assemble a large library of novel excited-state intramolecular proton transfer (ESIPT) fluorophores. The resulting 7-(pyrrol-2-yl)TAPs only show the enol-form emission, while 7-(indol-2-yl)TAPs would undergo an ESIPT process and mainly exhibit the keto-form emission. In highly polar solvents, the enol-form emission of 7-(indol-2-yl)TAPs is enhanced significantly, thus showing the dual emission of enol and keto forms.
Suppressing aggregation-caused quenching (ACQ) effect and reducing device efficiency roll-off are both crucial yet challenging for multi-resonance (MR) emitters. Herein, we put forward a medium-ring strategy to design efficient MR emitters that feature heptagonal tribenzo[b,d,f]azepine (TBA) donors. The highly twisted conformation enlarges the intermolecular distances between the MR-emitting cores, and thus suppresses ACQ effect. Meanwhile, the introduction of heptagonal donors enhances spin-orbital coupling, so as to accelerate reverse intersystem crossing (RISC) process. This medium-ring strategy gives rise to the first example of blue MR emitter that simultaneously possesses radiative decay rate as fast as 10 8 s À 1 and RISC rate as fast as 10 6 s À 1 . Accordingly, DTBA-B2N3 enables to assemble high-performance blue organic light-emitting diodes (OLEDs) with maximum external quantum efficiency (EQE max ) of 30.9 % and alleviated efficiency roll-off (EQE 1000 : 20.5 %).
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