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Multi‐resonance TADF (MR‐TADF) emitters are promising for high‐resolution OLEDs, but the concurrent optimization of excited‐state dynamics and color purity remains a tough challenge. Herein, three deep‐blue MR‐TADF compounds (BN1–BN3) featuring gradually enlarged ring‐fused structures and increased rigidity are accessed by lithium‐free borylation in high yields from the same precursor, with all the emitters possessing CIEy coordinates below 0.08. Structure–property investigations demonstrate a strategic improvement of the oscillator strength (fosc) and acceleration of the reverse intersystem crossing (RISC) process by extending the π‐skeleton, where BN3 realizes a maximum external quantum efficiency (EQE) of 37.6 % and reduced roll‐off, thus showing the best efficiency reported for deep‐blue TADF OLEDs. The internal regulation of the efficiency and color purity of these compounds validate the general effectiveness to achieve advanced deep‐blue narrowband emitters with higher‐order boron/nitrogen‐based MR motifs. [ABSTRACT FROM AUTHOR]

Non‐doped organic light‐emitting diodes (OLEDs) are particularly appealing due to the merit of the extremely simple device structure. However, the performance of non‐doped OLEDs is usually far inferior than that of doped devices, mainly due to the lack of desirable emitters. An ideal emitter for non‐doped OLEDs should not merely be highly emissive in the host matrix but also be capable of delivering excellent properties in its condensed state. Herein, through molecular engineering, an "axial and equatorial carbazolyl extension" approach to manipulate the molecular packing behavior is developed, and thus, the emitter is awarded with superior properties in its neat film. Based on this approach, through simply modifying the conventional acridine donor in a thermally activated delayed fluorescence (TADF) emitter with carbazole moieties in the way of hyper‐conjugation, two new TADF emitters with the molecular skeleton being extended both horizontally and vertically by carbazole moieties are constructed. The resulted TADF emitters reveal superb properties with simultaneous excellent thermal and morphological stabilities, photophysical behaviors, and charge transporting ability in their neat film. Owing to the merits of these synergistic superior properties, highly efficient non‐doped green emissive OLED with the state‐of‐the‐art external quantum efficiency of nearly 30% is realized. [ABSTRACT FROM AUTHOR]

Doping sensitivity is a great obstacle in boosting thermally activated delayed fluorescence (TADF)‐based organic light‐emitting diodes into practical application. Herein, a "side by side" donor alignment strategy is proposed to achieve decent electroluminescence performance under high doping concentration by studying the structure–property relationship of two emitters D2T‐TRZ and D2Y‐TRZ. D2T‐TRZ containing parallel aligned donors shows high photoluminescent quantum yield (PLQY) and short delayed lifetime (τd) in both doped and neat films, which endow its excellent performances with maximum external quantum efficiencies (EQEmaxs) higher than 22% under wide doping range of 10–70 wt%. While, composed of antiparallel acridans, D2Y‐TRZ presents good PLQY and relatively long τd when diluted in host matrix, but undergoes severe quenching in neat films. Consequently, D2Y‐TRZ achieves lower EQEmaxs of 14.9–16.4% within narrow range of 10–40 wt%. This result reveals parallel aligned donors as a better choice to design TADF emitters inert to doping concentration. [ABSTRACT FROM AUTHOR]

Multi‐resonance thermally activated delayed fluorescence (MR‐TADF) offers an exceptional solution for narrowband organic light‐emitting diode devices in terms of color purity and luminescence efficiency, while the development of new MR skeleton remains an exigent task. It is hereby demonstrated that a simple modification of the B (boron)−N (nitrogen) framework by sp3‐carbon insertion will significantly bathochromic shift the short‐range charge‐transfer emission, boost the reverse intersystem crossing process, and improve the device performances. The bis(acridan)phenylene‐based skeleton developed in this contribution presents a non‐planar conformation with functional sites to facilely introduce isolating units, deriving two luminophores with quantum yields approaching 90% in film state and narrowband emission. Corresponding green‐emissive devices realize superior performances compared to the planar carbazolyl‐based MR‐TADF analogs, featuring a maximum external quantum efficiency (EQEmax) up to 28.2% and small efficiency roll‐off without the involvement of any sensitizing host. [ABSTRACT FROM AUTHOR]

Organic light‐emitting diodes (OLEDs) with simple nondoped device structure are extremely attractive for real applications since excitons can be utilized without considering the possible charge trapping and morphology issues in the host–dopant systems. Emitters with suppressed concentration annihilation capability are essential for nondoped devices. Herein, two thermally activated delayed fluorescence (TADF) emitters based on a novel 3D electron donor, namely, TDMAC, are constructed. The TDMAC donor consists of a conventional donor with fused triptycene scaffold. Benefitting from the unique rigid and bulky triptycene moiety, these TADF emitters exhibit excellent thermal, morphological, and photophysical properties. Consequently, highly efficient OLEDs with external quantum efficiencies up to 24.2% and 23% are realized for doped and nondoped devices, respectively. [ABSTRACT FROM AUTHOR]

Spiro‐acridan (SpA) derivatives possess a great potential in preparing efficient thermally activated delayed fluorescent (TADF) emitters. However, the conventional synthetic routes are cost‐expensive and time‐consuming. The development of a simple procedure to synthesize SpAs is still in urgent pursuing appreciated by academic and industrial communities. In this contribution, we present a feasible acid‐catalyzed solvent‐free metal‐free cyclization between diarylamines and ketones to construct SpAs. The as‐constructed moieties provide a wide possibility to assemble efficient TADF emitters. As an example, D2T‐TR with high photoluminescent quantum yield and proper TADF character is applied in organic light emitting diodes (OLEDs) which achieves a maximum external quantum efficiency (EQE) of 27.1 %. This work shows us a bright inspiration on developing excellent organic optoelectronic materials and an effective tool to realize it. [ABSTRACT FROM AUTHOR]

[Display omitted] • Molecular engineering by linear extension resulted in two blue TADF emitters. • The two emitters exhibited high photoluminescence quantum yields and preferred horizontal dipole orientation. • Deep-blue TADF OLEDs achieved external quantum efficiency of up to 29.3% and low efficiency roll-off. Highly efficient blue thermally activated delayed fluorescence (TADF) materials with high horizontal dipole orientation (Θ //) remain a big challenge due to the concentration quenching effects and serious efficiency roll-offs in their corresponding organic light-emitting diodes (OLEDs). We herein report two novel TADF compounds, namely 2TDBA-SBA and TDBA-SBA, which were facilely synthesized by utilizing a rigid oxygen-bridged cyclized triarylboron-based unit (TDBA) as the acceptor and a spiro acridine (SBA) as the donor. Benefiting from the rigid and planar skeleton of the acceptor and the linear molecular shape, high Θ // s and photoluminescence quantum yields (PLQYs) of ∼ 90% were achieved. Significantly, TDBA-SBA exhibited excellent TADF properties with a short delayed fluorescence lifetime of only 684 ns and narrow full-width at half-maximum (FWHM) of 44 nm in solution state, accompanied by the high PLQYs of over 80% at high doping concentrations, manifesting the alleviated exciton quenching effects. Consequently, OLEDs based on TDBA-SBA achieved a high maximum external quantum efficiency (EQE) of 29.3% and a maximum brightness of 27663 cd cm−2. Importantly, an EQE over 20% was realized even at the high brightness of 10000 cd cm−2, signifying a small efficiency roll-off. [ABSTRACT FROM AUTHOR]

The development of the thermally activated delayed fluorescence (TADF) emitters with circularly polarized luminescence (CPL), particularly those exhibiting deep-blue emission is still a formidable challenge. In this work, we reported a simple and easily accessed molecular design strategy for deep-blue circularly polarized TADF (CP-TADF) enantiomers. Two chiral compounds, namely (S)-NPE-AcDPS and (R)-NPE-AcDPS, were successfully designed and synthesized, which featured concurrently TADF, CPL, and aggregation-induced enhanced emission (AIEE) properties. The CPL exhibited a maximum g PL value of 3.0 × 10−4. These emitters exhibited deep blue emission peaking at 451 nm in doped film with a high photoluminescence of 86% and a small singlet-triplet splitting of 0.05 eV. Furthermore, the deep blue OLED based on (S)-NPE-AcDPS demonstrated a high external quantum efficiency (EQE) up to 18.5%. [Display omitted] • Rigidifying the two phenyls of the famous emitter DMAC-DPS with a chiral bridge unit resulted in two blue TADF emitters. • The emitters exhibited high photoluminescence quantum yields, excellent TADF properties and obvious chiroptical activities. • Deep-blue TADF organic light-emitting diodes achieved external quantum efficiency of up to 18.5%. [ABSTRACT FROM AUTHOR]

[Display omitted] • Narrowband green emitters are successfully achieved by multi-resonance boron-nitrogen framework. • Heavy-atom effect of sulfur was beneficial to accelerate the reverse intersystem crossing. • Green organic light-emitting diodes with high external quantum efficiency up to 25.5% are achieved. As one type of latest emitters with simultaneous high efficiency and color-purity, the development of multi-resonance thermally activated delayed fluorescence (MR-TADF) materials represents an important advancement for organic light-emitting diodes (OLEDs). We herein present a new strategy to improve the performance of MR-TADF emitters by fusing sulfur element into the B-N based framework, aiming to utilize the non-metal heavy-atom effect in accelerating the reverse intersystem crossing (RISC) process of the emitter. Two compounds, namely 2PTZBN and 2PXZBN, were developed in this work through rigidifying the DABNA-1 skeleton by sulfur or oxygen atoms. The theoretical calculations and photoluminescence studies reveal that the sulfur-incorporated 2PTZBN enable considerable rate constant of RISC (k RISC) up to 2.8 × 105 s−1 in toluene due to larger spin-orbital coupling (SOC) values and smaller singlet–triplet energy splitting (Δ E ST) compared with 2PXZBN. Consequently, organic light-emitting diodes based on 2PTZBN exhibited highly efficient green emission with maximum external quantum efficiency (EQE) of 25.5%. [ABSTRACT FROM AUTHOR]

• Molecular engineering by σ-bond spacer is adopted for designing new host materials for the TADF emitter. • The newly developed host materials exhibit excellent solution processability and high triplet energy levels over 2.8 eV. • Host material with the lowest polarity achieves the highest reverse intersystem crossing rate. • Solution-processed TADF devices with a maximum external quantum efficiency up to 21.6% are demonstrated. High-performance solution-processable host materials for thermally activated delayed fluorescence (TADF) emitters are of great significance to the development of organic light-emitting diodes (OLEDs). In this study, three solution-processable hosts, namely mCP-Ph, mCP-Py, and mCP-BmPy featuring a basic structure paradigm of donor-σ-acceptor (D-σ-A) are reported for green TADF OLEDs. Attributing to the well-designed structure, the three host materials exhibited high triplet energy levels and excellent solution processability. It was found that the host materials had a significant impact on the excited state characteristics of the TADF emitter, and the mCP-Ph host with the lowest dipole moment showed the highest intersystem crossing rate constants (k ISC and k RISC). In consequence, solution-processed TADF OLEDs based on the emitter 4-(4-(9,9-dimethylacridin-10(9 H)-yl)phenyl)-2,6-diphenylpyridine-3,5-dicarbonitrile (DMAC-PCN) and the host 9-(3-(9 H -carbazol-9-yl)phenyl)-3-(2,7-di- tert -butyl-9-phenyl-9 H -fluoren-9-yl)-9 H -carbazole (mCP-Ph) secured a maximum external quantum efficiency of 21.6%, demonstrating the effectiveness of the host engineering by σ-spacer. This work reveals the important principle for designing bespoke host for TADF emitters. [ABSTRACT FROM AUTHOR]