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Organic thermally activated delayed fluorescence (TADF) materials have attracted significant research interest in the field of organic electronics because of their inherent advantage of 100% exciton utilization capability in organic light‐emitting diodes (OLEDs) without the use of noble metals. However, despite their high internal electroluminescence quantum efficiencies approaching unity, broad emission spectra with sizable full width at half maxima (FWHM; 60–100 nm) present a critical issue that must be solved for their application in ultrahigh‐definition OLED displays. Recently, a new paradigm of TADF materials featuring the multiple resonance (MR) effect based on heteroatom‐doped polycyclic aromatic frameworks, referred to as MR‐TADF materials, has emerged and garnered considerable research interest owing to their remarkable features of efficient narrowband emissions with extremely small FWHMs (≤30 nm). Currently, MR‐TADF materials occupy a prominent position in the cutting‐edge research on organic light‐emitting materials from both chemical and physical perspectives. This review article focuses on recent progress in narrowband emissive MR‐TADF systems from the perspective of molecular design, photophysical properties, and electroluminescence performance in OLEDs. The current status and future prospects of this advanced material technology are discussed comprehensively. [ABSTRACT FROM AUTHOR]

Ultra‐deep‐blue aggregation‐induced delayed fluorescence (AIDF) emitters (TB‐tCz and TB‐tPCz) bearing organoboron‐based cores as acceptors and 3,6‐substituted carbazoles as donors are presented. The thermally activated delayed fluorescence (TADF) properties of the two emitters are confirmed by theoretical calculations and time‐resolved photoluminescence experiments. TB‐tCz and TB‐tPCz exhibit fast reverse intersystem crossing rate constants owing to efficient spin–orbit coupling between the singlet and triplet states. When applied in solution‐processed organic light‐emitting diodes (OLEDs), the TB‐tCz‐ and TB‐tPCz‐based nondoped devices exhibit ultra‐deep‐blue emissions of 416–428 nm and high color purity owing to their narrow bandwidths of 42.2–44.4 nm, corresponding to the Commission International de l´Eclairage color coordinates of (x = 0.16–0.17, y = 0.05–0.06). They show a maximum external quantum efficiency (EQEmax) of 8.21% and 15.8%, respectively, exhibiting an unprecedented high performance in solution‐processed deep‐blue TADF‐OLEDs. Furthermore, both emitters exhibit excellent device performances (EQEmax = 14.1–15.9%) and color purity in solution‐processed doped OLEDs. The current study provides an AIDF emitter design strategy to implement high‐efficiency deep‐blue OLEDs in the future. [ABSTRACT FROM AUTHOR]

In this study, two host materials, pCzBzbCz and pCzPybCz, are synthesized to achieve a high efficiency and long lifetime of blue thermally activated delayed fluorescence organic light‐emitting diodes (TADF‐OLEDs). The molecular design strategy involves the introduction of a pyridine group into the core structure of pCzPybCz as an electron‐withdrawing unit, and an electron‐donating phenyl group into the structure of pCzBzbCz. These host materials demonstrate good thermal stability and high triplet energy (T1=3.07 eV for pCzBzbCz and 3.06 eV for pCzPybCz) for the fabrication of blue TADF‐OLEDs. In particular, pCzPybCz‐based OLED devices demonstrate an external quantum efficiency (EQE) of 22.7 % and an operational lifetime of 24 h (LT90, time to attain 90 % of initial luminance) at an initial luminance of 1000 cd m−2. This superior lifetime could be explained by the C−N bond dissociation energy (BDE) in the host molecular structure. Furthermore, a mixed‐host system using the electron‐deficient 2,4‐bis(dibenzo[b,d]furan‐2‐yl)‐6‐phenyl‐1,3,5‐triazine (DDBFT) is proposed to inhibit the formation of the anion state of our host materials. In short, the device operational lifetime is further improved by applying DDBFT. The carbazole‐based asymmetric host molecule containing a pyridine core realizes a high‐efficiency blue TADF‐OLED showing a positive effect on the operating lifetime, and can provide useful strategies for designing new host materials. [ABSTRACT FROM AUTHOR]

Three new color‐tunable (deep‐blue to sky‐blue) and solution‐processable emitters—9′‐(2,12‐di‐tert‐butyl‐5,9‐dioxa‐13b‐boranaphtho[3,2,1‐de]anthracen‐7‐yl)‐9′H‐9,3′:6′,9″‐tercarbazole (TB‐3Cz), 9′‐(2,12‐di‐tert‐butyl‐5,9‐dioxa‐13b‐boranaphtho[3,2,1‐de]anthracen‐7‐yl)‐9,9″‐diphenyl‐9H,9′H,9″H‐3,3′:6′,3″‐tercarbazole (TB‐P3Cz), and 9‐(2,12‐di‐tert‐butyl‐5,9‐dioxa‐13b‐boranaphtho[3,2,1‐de]anthracen‐7‐yl)‐N3,N3,N6,N6‐tetraphenyl‐9H‐carbazole‐3,6‐diamine (TB‐DACz)—are demonstrated, which are cleverly designed and synthesized by appending a boron‐fused entity as an electron acceptor to different electron‐rich entities containing carbazole derivatives as donors. The thermal, photophysical, electrochemical, and electroluminescent characteristics of all the new materials are extensively investigated. Comprehensive photophysical investigations reveal that these emitters exhibit not only thermally activated delayed fluorescence (TADF) but also aggregation‐induced emission (AIE) properties. Consequently, solution‐processable organic light‐emitting diodes (OLEDs) fabricated using these new materials as nondoped emitters in the emissive layer exhibit a maximum external quantum efficiency (EQE) and Commission Internationale de l'Éclairage (CIE) color coordinates of 9.90% and (0.17, 0.07), respectively, for TB‐3Cz; 6.13% and (0.15, 0.08), respectively, for TB‐P3Cz; and 6.04% and (0.18, 0.40), respectively, for TB‐DACz. As far as it is known, the performance and ultrahigh color purity satisfying the deep‐blue CIE coordinates of the National Television System Committee (NTSC) for TB‐3Cz and TB‐P3Cz are the highest reported thus far for nondoped solution‐processable TADF emitters, indicating the great potential of these materials as deep‐blue luminogens in OLED applications. [ABSTRACT FROM AUTHOR]

A new solution processable cruciform tetraphenylsilane-based bipolar host material, bis(4-(9 H -carbazol-9-yl)phenyl)bis(4-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)silane (SiCT), was designed and synthesized. Two carbazoles as donors and two diphenyl triazine moieties as acceptors were tethered to the tetraphenylsilane. SiCT showed great solubility in common organic solvents, high thermal stability, high triplet energy (T 1 ∼3.0 eV), and a superior bipolar electronic nature, which are sufficient for it to function as a host material in thermally activated delayed fluorescence organic light emitting diodes (TADF-OLEDs). Consequently, the solution-processed green TADF-OLEDs employed SiCT as a bipolar host exhibited a low turn-on voltage and high external quantum efficiency (EQE) of 19.17% with a high power efficiency (PE) of 41.13 lm W−1, while control device based-on SiC as unipolar host showed a low EQE of 12.74% with a low PE of 16.13 lm W−1. This work highlights the potential of a bipolar tetraphenylsilane derivative as a host material in solution-processable green TADF-OLEDs. Image 1 • The cruciform host material SiCT with silane core was designed and synthesized. • SiCT showed high solubility, high thermal stability, high triplet energy, and a superior bipolar electronic nature. • The solution-processed green TADF-OLEDs employed SiCT exhibited a low turn-on voltage and a high EQE of 19.17%. [ABSTRACT FROM AUTHOR]