In this work, we propose pure hydrocarbon materials as universal hosts for high-efficiency red, green and blue phosphorescent organic light-emitting diodes.

Rational manipulation of frontier orbital distribution and singlet‐triplet splitting is crucial to exploit the luminescent properties of organic molecules. To realize ultra‐blue luminescence, both blue‐shifted wavelength peak (λpeak) and narrow full‐width at half‐maximum (FWHM) are required. Herein, a new thermally activated delayed fluorescence (TADF) skeleton by inserting the diphenyl methylene intramolecular‐lock to adjust the torsion angles and restrict the intramolecular relaxation is developed. Two rigid emitters, incorporating phenoxazine (PXZN‐B) and acridine (DMACN‐B) as donors and mesitylboron as an acceptor, exhibit narrow FWHMs (<50 nm) with deep‐blue (0.133, 0.147) and violet‐blue emission (0.151, 0.045), respectively. In particular, the Commission Internationale de l'Eclairage (CIE) coordinates of a DMACN‐B‐based device closely approach the Rec.2020 standard (0.131, 0.046). Moreover, both of the organic light‐emitting diodes (OLEDs) based on PXZN‐B and DMACN‐B show TADF character, with high external quantum efficiencies (EQEs) exceeding 10%. Furthermore, owing to the large orbital overlap, these TADF emitters own a fast S1–S0 transition rate exceeding 108 s–1, thereby exhibiting marked amplified spontaneous emission (ASE) with low thresholds. Therefore, the intramolecular‐lock strategy provides not only innovation for realizing high‐efficiency deep‐blue TADF emission with high color purity but also an avenue for a TADF‐based ASE and lasing application.

A multiple resonance thermally activated delayed fluorescence (MR‐TADF) molecule with a fused, planar architecture tends to aggregate at high doping ratios, resulting in broad full width at half maximum (FWHM), redshifting electroluminescence peaks, and low device efficiency. Herein, we propose a mono‐substituted design strategy by introducing spiro‐9,9′‐bifluorene (SBF) units with different substituted sites into the MR‐TADF system for the first time. As a classic steric group, SBF can hinder interchromophore interactions, leading to high device efficiency (32.2–35.9 %) and narrow‐band emission (≈27 nm). Particularly, the shield‐like molecule, SF1BN, seldom exhibits a broadened FWHM as the doping ratio rises, which differs from the C3‐substituted isomer and unhindered parent emitter. These results manifest an effective method for constructing highly efficient MR‐TADF emitters through a spiro strategy and elucidate the feasibility for steric modulation of the spiro structure in π‐framework.

A narrowband blue CP-TADF emitter with a rigid hetero-helicene structure (QAO-PhCz) was synthesized and characterized. QAO-PhCz exhibits good electroluminescence performance (EQE = 14.0%) and narrow FWHM. The enantiomers of QAO-PhCz...

To date, all efficient host materials reported for phosphorescent OLEDs (PhOLEDs) are constructed with heteroatoms, which have a crucial role in the device performance. However, it has been shown in recent years that the heteroatoms not only increase the design complexity but can also be involved in the instability of the PhOLED, which is nowadays the most important obstacle to overcome. Herein, we design pure aromatic hydrocarbon materials (PHC) as very efficient hosts in high-performance white and blue PhOLEDs. With EQE of 27.7 %, the PHC-based white PhOLEDs display similar efficiency as the best reported with heteroatom-based hosts. Incorporated as a host in a blue PhOLED, which are still the weakest links of the technology, a very high EQE of 25.6 % is reached, surpassing, for the first time, the barrier of 25 % for a PHC and FIrpic blue emitter. This performance shows that the PHC strategy represents an effective alternative for the future development of the OLED industry.

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A novel donor (D)–spiro-acceptor (A) emitter, namely 10-phenyl-10H-spiro[acridine-9,9′-fluorene]-2′,4′,7′-tricarbonitrile (SAF-3CN), was synthesized for high efficiency, yellowish green third-generation thermally activated delayed fluorescence (TADF) organic light-emitting diodes (OLEDs).

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