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Despite the remarkable multiple resonance (MR) optoelectronic properties of organic nanographenes with boron and nitrogen atoms disposed para to each other, the synthetic procedures are sophisticated with low yields and the molecular skeletons are limited. Here, a new paradigm of easy‐to‐access MR emitter is constructed by simplifying the multiborylation through amine‐directed formation of B−N bonds while introducing an additional para‐positioned nitrogen atom to trigger the MR effect. The proof‐of‐concept molecules exhibit narrowband emissions at 480 and 490 nm, with full width at half maxima (FWHMs) of only 29 and 34 nm. The devices based on them showed external quantum efficiencies (EQE) of >33.0 %, which remained above 24.0 % even at a high brightness of 5000 cd m−2. This is the first example of MR emitters with a B−N covalent bond, not only decreasing the synthesis difficulty but also increasing the diversity of MR skeletons for emerging new optoelectronic properties. [ABSTRACT FROM AUTHOR]

Polycyclo‐heteraborin multi‐resonance (MR) emitters are promising for high color‐purity organic light‐emitting diodes (OLEDs). Here, unlike the most common heteroatom ternary‐doped (X/B/N) frameworks, a binary‐doped (B/N) skeleton is reported with a large energy band for wide‐range color tunability. Based on this parent‐segment, a "one‐pot" catalyst‐free borylation method is developed which generates deep blue to pure green MR emitters from readily available starting materials, with peaks at 426–532 nm and full‐width‐at‐half‐maxima of 27–38 nm. Impressively, a maximum external quantum efficiency of nearly 40 % is recorded for the corresponding device with Commission Internationale de l′Eclairage coordinates of (0.14, 0.16), representing the state‐of‐the‐art performances. This work presents a new paradigm and synthesis of B/N‐doped MR emitters and will motivate the study of other novel frameworks. [ABSTRACT FROM AUTHOR]

Herein, we report a general strategy for achieving ultra‐pure green emissions by suppressing the shoulder peaks in the emission spectra of conventional polycyclic aromatic hydrocarbons (PAHs). Through precise synthetic fusion of multi‐resonance (MR) fragments with conventional PAH, extended π‐conjugation lengths, increased molecular rigidity, and reduced vibrational frequency could be simultaneously realized. The proof‐of‐concept emitters exhibited ultra‐pure green emissions with dominant peaks at ca. 521 nm, photoluminescence quantum yields that are greater than 99 %, a small full‐width‐at‐half‐maximum of 23 nm, and CIE coordinates of (0.16, 0.77). The bottom‐emitting organic light‐emitting diode (OLED) exhibited a record‐high CIEy value of 0.74 and a high maximum external quantum efficiency of 30.5 %. The top‐emitting OLED not only achieved a BT.2020 green color (CIE: 0.17, 0.78) for the first time but also showed superior performance among all green OLED devices, with a current efficiency of 220 cd A−. [ABSTRACT FROM AUTHOR]

Nitrogen‐containing polycyclic heteroaromatics have exhibited fascinating multi‐resonance (MR) characteristics for efficient narrowband emission, but strategies to bathochromic shift their emissions while maintaining the narrow bandwidths remain exclusive. Here, homogeneous hexatomic rings are introduced into nitrogen‐embedded MR skeletons to prolong the π‐conjugation length for low‐energy electronic transitions while retaining the non‐bonding character of the remaining parts. The proof‐of‐the‐concept emitters exhibit near unity photoluminescence quantum yields with peaks at 598 nm and 620 nm and small full‐width‐at‐half‐maximums of 28 nm and 31 nm, respectively. Optimal organic light‐emitting diodes exhibit a high external quantum efficiency of 18.2 %, negligible efficiency roll‐off, and ultra‐long lifetime with negligible degradation at an initial luminance of 10 000 cd m−2 after 94 hours. [ABSTRACT FROM AUTHOR]

Fused twin-acridine scaffolds of TMQAC and MeTMQAC were designed as novel donors to construct new organic emitters. TMQAC-based emitters were TADF active, while the TADF character was turned off in MeTMQAC-based emitters by the extra methyl group. The TMQAC-based emitters exhibited high OLED performances, with external quantum efficiencies (EQEs) of up to 20.7%. [ABSTRACT FROM AUTHOR]

Light out-coupling has been a long-lasting issue for organic light-emitting devices (OLEDs). Aside from light extraction schemes relying on generally complicated optical structures, the most convenient and desirable approach, however, is to directly enhance light extraction through modulating optical properties of active layers in conventional planar OLEDs. Here, we report the adoption of a high refractive index transparent electrode as a new avenue for greatly boosting OLED light extraction efficiency. By using the Nb-doped TiO 2 transparent electrodes with a high refractive index of 2.4, along with state-of-the-art low-index organic carrier transporters and highly horizontal dipole emitters, a very high external quantum efficiency of exceeding 40% (41.5%) is realized for simple, conventional planar OLEDs. As a perspective, simulation also predicts extremely high optical out-coupling efficiency approaching or exceeding 70% with conventional planar OLEDs, if even higher-index transparent electrodes, purely horizontal dipole emitters, and even lower-index carrier transporters can be realized. The results of this work manifest simple device architectures for extremely efficient OLEDs, and are believed to provide useful guidelines regarding future development of materials and devices for extremely efficient OLEDs. Image 1 • Combining high-index transparent electrode, low-index organic layers, and horizontally oriented emitters to enhance light extraction in OLEDs. • Successful development and use of high-index Nb-doped TiO 2 transparent anodes for OLEDs. • Demonstrating very high external quantum efficiency of up to 41.5% with simple planar device structures. [ABSTRACT FROM AUTHOR]

[Display omitted] • Highly efficient TADF emitters were synthesized with star-shaped architecture. • Both emitters exhibited high PLQYs and horizontal emitting dipole orientations. • The EQE of near 39% represented the record-high efficiency for green TADF OLED. • The EQE remained as high as 30.3% at 1000 cd/m2 with low efficiency roll-off. The combination of acridine/phenoxazine donors and triarylboron acceptor has afforded two thermally activated delayed fluorescence (TADF) emitters with D 3 -A typed architectures, namely 3DMAC-TB and 3PXZ-TB. Attributing to the highly steric hindrance between D/A groups as well as intense intramolecular charge transfer state, both emitters exhibit well-separated frontier molecular orbitals (FMOs) distributions and distinct TADF characteristics. The high rigidity molecular structures of 3DMAC-TB and 3PXZ-TB contribute to high photoluminescence quantum yields (PLQYs) up to 0.94 and 0.89, respectively. The "star-shaped" configuration endows both emitters with high ratios of horizontal dipole orientation of 86% and 80%, respectively. The organic light emitting diodes (OLEDs) involving 3DMAC-TB and 3PXZ-TB as emitting dopants achieve maximum external quantum efficiencies of 38.8% and 29.4%, respectively. The efficiency of 3DMAC-TB based device is among the state-of-the-art efficiency for green TADF OLEDs. This work unveils great potential with triarylboron-cored multi-donors molecular design strategy in the development of excellent TADF molecules simultaneously possessing high quantum yields and preferentially horizontal emitting dipole orientations. [ABSTRACT FROM AUTHOR]

Although both high-index substrates and horizontal-dipole emitters have been shown to be facile approaches for enhancing OLED (organic light emitting diode) light extraction, the full benefits and potential of their combination for OLED optical out-coupling have not been thoroughly studied and explored. Simulation studies indicate that very high optical coupling efficiency into substrates ϕ sub (and perhaps similarly high OLED external quantum efficiencies) of ~90% can be possibly obtained with both high-index substrates (refractive index >1.8–1.9) and highly horizontal-dipole emitters (horizontal dipole ratio >85%), together with adoption of low-index or index-matching carrier transport layers and optimization of organic layer and transparent electrode thicknesses. With these judicious device design conditions, all waveguided modes and surface plasmon modes in devices can be effectively suppressed for optimal optical out-coupling. Finally, combining the sapphire substrate having high index of n~ 1.78, the recently developed OLED emitters having high horizontal emitting dipole ratio of up to 87%, and simple external extraction lens, OLED devices having external quantum efficiency of over 80% was successfully realized. Image 1 • Combination of high-index substrates and horizontal dipole emitters can render very high EQE of up to 90% in OLED. • Together with index-matching organic layers and optimized thickness, all waveguided and surface plasmon modes can be suppressed. • Demonstrated high EQE of up to 80.8% using the sapphire substrate, highly horizontal emitters, and external extraction lens. [ABSTRACT FROM AUTHOR]