Herein, we report two multiple-resonance thermally activated delayed fluorescence emitters (VTCzBN and TCz-VTCzBN) based on indolo[3,2,1jk]carbazole unit and boron-nitrogen skeletons, whose emissions peaking at 496 and 521 nm with full width at half maximum of 34 and 29 nm, respectively. Meanwhile, fast rate constants of reverse intersystem crossing of above 10 6 s À 1 are obtained due to small singlet-triplet energy gaps and large spin-orbital coupling values. Notably, planar molecular structures along the transition dipole moment direction endow them with high horizontal emitting dipole ratios of up to 94 %. Consequently, the corresponding organic light-emitting diodes (OLEDs) show the maximum external quantum efficiencies of 31.7 % and 32.2 %, respectively. Particularly, OLED with TCz-VTCzBN display ultra-pure green emission with Commission Internationale de l'Eclairage coordinates of (0.22, 0.71), consistent with the green display standard of the National Television System Committee.

The data that support the findings of this study are available in the supplementary material of this article.

The maximum external quantum efficiency and external quantum efficiency measured at 100 and 1000 cd m −2 ; e) Maximum power efficiency; f) g EL around maximum emission.

The simultaneous achievement of multiple‐resonance thermally activated delayed fluorescence (MR‐TADF) materials with strong narrowband emission and efficient reverse intersystem crossing (RISC) process can further promote the advancement of organic light‐emitting diodes (OLEDs). Herein, a new strategy is proposed to achieve two π‐extended MR‐TADF emitters (NBO and NBNP) peaking at 487 and 500 nm via fusing conjugated high‐triplet‐energy units (carbazole, dibenzofuran) into boron‐nitrogen (B/N) framework, aiming to increase charge transfer delocalization of the B/N skeleton and minimize singlet‐triplet energy gap (∆EST). This strategy endows the two emitters with full width at half maximum of 27 and 29 nm, and high photoluminescence efficiencies above 90% in doped films, respectively. Additionally, considerable rate constants of RISC are obtained due to the small ∆EST (0.12 and 0.09 eV) and large spin‐orbital coupling values. Consequently, the OLEDs based on NBO and NBNP show the maximum external electroluminescence quantum efficiency of up to 26.1% and 28.0%, respectively, accompanied by low‐efficiency roll‐off. These results provide a feasible design strategy to construct efficient MR‐TADF materials for OLEDs with suppressed efficiency roll‐off.

Highly efficient multi-resonance thermally activated delayed fluorescence (MR-TADF) emitters with narrowband emissions based on B (boron)/ N (nitrogen) framework are crucial for next-generation full-color display with high color purity. This...

Multiple‐resonance thermally activated delayed fluorescence (MR‐TADF) emitters with highly planar and rigid skeleton tend toward self‐quenching and spectral broadening caused by strong inter‐chromophore interactions at high doping ratios. Herein, by introducing the sterically hindered unit (N‐phenylcarbazole) at the para‐ and meta‐positions of boron/nitrogen (B/N) framework (p−1‐PCzBN and m−1‐PCzBN), the face‐to‐face steric modulation between the non‐conjugated benzene ring and B/N skeleton is achieved to separate adjacent MR‐TADF skeletons and to suppress self‐quenching and spectral broadening. Consequently, the p−1‐PCzBN and m−1‐PCzBN emitters based organic light‐emitting diodes (OLEDs) show the maximum external quantum efficiency (EQEmax) values of up to 33.6% and 32.6% with full width at half maximum (FWHM) bands of 26 and 30 nm for electroluminescence (EL), respectively. Remarkably, the doped concentration has little effect on the device efficiency and FWHM of the EL, and this phenomenon is seldom reported for OLEDs based on MR‐TADF materials. Even at doping ratio of 30 wt%, the EQEs are still retained to be 28.5% and 25.6% with nearly unchanged electroluminescence spectra. These results manifest an effective strategy for constructing efficient doping concentration independent OLEDs through face‐to‐face steric modulation.

By inserting tricoordinate B atom into an indolo[3,2,1-jk]carbazole precursor, an efficient fused multiple resonance induced thermally activated delayed fluorescence emitter were prepared, which exhibits a narrowband emission and a considerable...

Herein, we report two multiple-resonance thermally activated delayed fluorescence emitters (VTCzBN and TCz-VTCzBN) based on indolo[3,2,1jk]carbazole unit and boron-nitrogen skeletons, whose emissions peaking at 496 and 521 nm with full width at half maximum of 34 and 29 nm, respectively. Meanwhile, fast rate constants of reverse intersystem crossing of above 10 6 s À 1 are obtained due to small singlet-triplet energy gaps and large spin-orbital coupling values. Notably, planar molecular structures along the transition dipole moment direction endow them with high horizontal emitting dipole ratios of up to 94 %. Consequently, the corresponding organic light-emitting diodes (OLEDs) show the maximum external quantum efficiencies of 31.7 % and 32.2 %, respectively. Particularly, OLED with TCz-VTCzBN display ultra-pure green emission with Commission Internationale de l'Eclairage coordinates of (0.22, 0.71), consistent with the green display standard of the National Television System Committee.