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Circularly polarized electroluminescence (CPEL) is highly promising in realm of 3D display and optical data storage. However, designing a groundbreaking chiral material with high comprehensive CPEL performance remains a formidable challenge. In this work, a pair of chiral polymers with self‐assembled behavior is designed by integrating a chiral BN‐moiety into polyfluorene backbone, named R‐PBN and S‐PBN, respectively. The chiral polymers show narrowband emission centered at 490 nm with full‐width half maximum (FWHM) of 29 nm and high photoluminescence quantum yield (PLQY) of 79 %. After thermal annealing treatment, the chiral polymers undergo self‐assembly, exhibiting amplified circularly polarized luminescence (CPL) with asymmetry factor (|glum|) of up to 0.11. Moreover, the solution‐processed nondoped CP‐OLEDs based on the chiral polymers as emitting layers exhibit maximum external quantum efficiency (EQEmax) of 9.8 %, intense CPEL activities with |gEL| of up to 0.07, and small FWHM of 36 nm, simultaneously. This represents the first case of self‐assembled chiral polymers that combines high EQE, large gEL value and narrowband emission. [ABSTRACT FROM AUTHOR]

It is of great strategic significance to develop highly efficient narrowband organic electroluminescent materials that can be utilized to manufacture ultra‐high‐definition (UHD) displays and meet or approach the requirements of Broadcast Television 2020 (B.T.2020) color gamut standards. This motif poses challenges for molecular design and synthesis, especially for developing generality, diversity, scalability, and robustness of molecular structures. The emergence of multiple resonance thermally activated delayed fluorescence (MR‐TADF) emitters has ingeniously solved the problems and demonstrated bright application prospects in the field of UHD displays, sparking a research boom. This Minireview summarizes the research endeavors of narrowband organic electroluminescent materials, with emphasis on the tremendous contribution of frontier molecular orbital engineering (FMOE) strategy. It combines the outstanding advantages of MR framework and donor‐acceptor (D−A) structure, and can achieve red‐shift and narrowband emission simultaneously, which is of great significance in the development of long‐wavelength narrowband emitters with emission maxima especially exceeding 500 nm. We hope that this Minireview would provide some inspiration for what could transpire in the future. [ABSTRACT FROM AUTHOR]

Organic semiconductors that emit by the process of multi‐resonance thermally activated delayed fluorescence (MR‐TADF) can deliver narrowband and efficient electroluminescence while being processable from solvents and metal‐free. This renders them attractive for use as the emitter in sustainable light‐emitting electrochemical cells (LECs), but so far reports of narrowband and efficient MR‐TADF emission from LEC devices are absent. Here, this issue is addressed through careful and systematic material selection and device development. Specifically, the authors show that the detrimental aggregation tendency of an archetypal rigid and planar carbazole‐based MR‐TADF emitter can be inhibited by its dispersion into a compatible carbazole‐based blend host and an ionic‐liquid electrolyte, and it is further demonstrated that the tuning of this active material results in a desired balanced p‐ and n‐type electrochemical doping, a high solid‐state photoluminescence quantum yield of 91%, and singlet and triplet trapping on the MR‐TADF guest emitter. The introduction of this designed metal‐free active MR‐TADF material into a LEC, employing air‐stabile electrodes, results in bright blue electroluminescence of 500 cd m−2, which is delivered at a high external quantum efficiency of 3.8% and shows a narrow emission profile with a full‐width‐at‐half‐maximum of 31 nm. [ABSTRACT FROM AUTHOR]

Narrowband emitters based on the multiple resonance (MR) effect have shown great promises for applications in high‐definition displays. Though most reported MR emitters adopt the boron‐ and nitrogen‐doped triangulene‐like skeleton following the design of the DABNA series, MR materials with the nitrogen‐only indolocarbazole structures have recently emerged and demonstrated good color tunability from violet to deep red and impressive electroluminescence performances in terms of both efficiency and stability. Herein, we will summarize indolocarbazole‐based MR materials in recent reports, with emphasis on their molecular design, synthesis, photophysical and electroluminescence properties as well as some future research directions to unlock the full potential of this fascinating class of materials. [ABSTRACT FROM AUTHOR]

[Display omitted] • The first high-performance chiral polarized UV organic light-emitting diode is reported. • A UV device displays a maximum external quantum efficiency of 7.2 % peaking at 396 nm. • The devices show excellent color purity and small efficiency roll-off. • Triplet exciton utility and large horizontal dipole ratios contribute to the excellent performance. • A molecular design strategy is provided for chiral ultraviolet organic emitters. Emitting circularly polarized electroluminescence (CPEL) directly endows the CP organic light-emitting diodes (CP-OLEDs) with great advantages in 3D display. But the highly efficient CP-OLEDs are still in great need, especially for devices emitting short-wavelength light such as ultraviolet (UV) CP-OLEDs. Herein, we report the first case of CP UV-OLED, fabricated by two pairs of enantiomers, (R)-/(S)-BNP- o -CzPI and (R)-/(S)-BNP- p -CzPI, established by chiral perturbation. Devices using 10 wt% enantiomers as dopants show UV CPEL at 396 nm with external quantum efficiency, Commission Internationale de l'Eclairage y value, and full width at half maxima of 7.2/6.9 %, 0.046/0.044 and 50/50 nm for (R)-/(S)-BNP- o -CzPI, respectively. The horizontal dipole orientations of the film with 10 wt% emitters in mCPCN are measured as high as 84.1/85.2 % and 88.1/88.7 % for (R)-/(S)-BNP- o -CzPI and (R)-/(S)-BNP- p -CzPI, respectively. Experiments and theoretical calculations indicate that the high EQEs are due to the high triplet exciton utility and large horizontal dipole orientation. In addition, the enantiomers show significant circularly polarized luminescence properties both in photoluminescence and in electroluminescence, and the device using (S)-BNP- o -CzPI has a large dissymmetry factors of 3.10 × 10−3 at emission maximum. [ABSTRACT FROM AUTHOR]

Narrowband emitting fluorophores exhibit immense potentials for organic light‐emitting diodes (OLEDs) with high color purity. However, it's still hard to simultaneously realize short‐wavelength ultraviolet (UV) or near ultraviolet emission (NUV) while maintaining a narrowed full width at half maximum (FWHM) value, and rare work focus on such challenging pursuit. Herein, an ingenious synthetic method was devised to achieve emitters with coplanar structure. 11‐(4,6‐diphenyl‐1,3,5‐triazin‐2‐yl)indolo[3,2,1‐jk]carbazole (ICZ‐TAZ) was designed to realize narrowed UV emission both in photoluminescence (PL) and electroluminescence (EL) which benefited from the suppression of vibronic coupling. UV/NUV OLEDs based on ICZ‐TAZ achieve external quantum efficiency (EQE) maximums of 3.26 % peaks @ 388 nm and 4.02 % peaks @ 406 nm with small FWHM of 32 nm and 46 nm, respectively, corresponding with reduced efficiency roll‐off at luminance of 100 cd m−2. [ABSTRACT FROM AUTHOR]

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]

Herein, a ternary boron‐oxygen‐nitrogen embedded polycyclic aromatic hydrocarbon with multiple resonance thermally activated delayed fluorescence (MR‐TADF), namely DBNO, is developed by adopting the para boron‐π‐boron and para oxygen‐π‐oxygen strategy. The designed molecule presents a vivid green emission with a high photoluminescence quantum yield (96 %) and an extremely narrow full width at half maximum (FWHM) of 19 nm/0.09 eV, which surpasses all previously reported green TADF emitters to date. In addition, the long molecular structure along the transition dipole moment direction endows it with a high horizontal emitting dipole ratio of 96 %. The organic light‐emitting diode (OLED) based on DBNO reveals a narrowband green emission with a peak at 504 nm and a FWHM of 24 nm/0.12 eV. Particularly, a significantly improved device performance is achieved by the TADF‐sensitization (hyperfluorescence) mechanism, presenting a FWHM of 27 nm and a maximum external quantum efficiency (EQE) of 37.1 %. [ABSTRACT FROM AUTHOR]

Thermally activated delayed fluorescence (TADF) materials based on multiple resonance (MR) effect exhibit enormous potentials in organic light‐emitting diodes (OLEDs) with high color purity due to their intrinsically narrow emission. However, most of MR‐TADF emitters are limited to the boron‐nitrogen‐based rigid skeleton. In this work, three novel MR‐TADF emitters, namely CzBNO, DMAcBNO and DPAcBNO, are elaborately constructed, the TADF properties of which are realized by virtue of opposite MR effect of boron and nitrogen/oxygen atom. CzBNO‐based deep blue‐emitting OLEDs achieve a maximum external quantum efficiency (EQE) of 13.6% with a small FWHM of 36 nm, as well as a Commission Internationale de l'Eclairage (CIE) coordinate of (0.14,0.08). While the other two emitter‐based devices exhibit blue emission with a maximum EQE of up to 23.0%. To further improve the OLEDs performances, DMAcBNO and DPAcBNO‐based devices assisted by a sensitizer exhibit an excellent EQE of up to 29.6% with a relatively small efficiency roll‐off. [ABSTRACT FROM AUTHOR]

Developing organic luminophores with unique capability of strong narrowband emission is both crucial and challenging for the further advancement of organic light‐emitting diodes (OLEDs). Herein, a nanographitic fused‐nonacyclic π‐system (BSBS‐N1), which was strategically embedded with multiple boron, nitrogen, and sulfur atoms, was developed as a new multi‐resonance thermally activated delayed fluorescence (MR‐TADF) emitter. Narrowband sky‐blue emission with a peak at 478 nm, full width at half maximum of 24 nm, and photoluminescence quantum yield of 89 % was obtained with BSBS‐N1. Additionally, the spin‐orbit coupling was enhanced by incorporating two sulfur atoms, thereby facilitating the spin‐flipping process between the excited triplet and singlet states. OLEDs based on BSBS‐N1 as a sky‐blue MR‐TADF emitter achieved a high maximum external electroluminescence quantum efficiency of 21.0 %, with improved efficiency roll‐off. [ABSTRACT FROM AUTHOR]

Thermally activated delayed fluorescence (TADF) materials that are able to realize electroluminescence showing simultaneously narrow emission band, high color purity, and high efficiency are highly demanded for display applications. Up to now, a few blue emissive TADF materials with such characteristics have been reported, while green TADF materials with such features are extremely scarce. Herein, two TADF compounds with highly efficient narrowband bluish green/green emission (full‐width at half‐maximum (FWHM): 22 and 21 nm in toluene) induced by multiple resonance effect are reported. An optimized organic light‐emitting diode based on the green emissive compound shows a fairly narrow electroluminescent spectrum (FWHM: 33 nm), as well as an excellent color purity with the Commission Internationale de L'Eclairage (CIE) coordinates of (0.20, 0.65), which is a close resemblance to the standard green‐light CIE coordinates of (0.21, 0.71) defined by the National Television System Committee. Meanwhile, the maximum external quantum efficiency (EQE) up to 25.5% is achieved and a high EQE of 20.1% is maintained at a practical high luminance of 1000 cd m−2. The outstanding device performance of the compound makes it attractive for potential practical applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • Novel host materials with dendritic architectures are developed for MR-TADF OLEDs. • Alkoxy-capping groups up-shift HOMO levels to realize barrier-free hole injection. • Adamantane core interrupts conjugation of four carbazole dendrons to keep high E T. • EQE of 24.2% is realized for solution-processed narrowband OLEDs using dendritic host. Narrowband electroluminescence from multi-resonance thermally activated delayed fluorescence (MR-TADF) emitters have attracted much attention owing to their potential in developing high-resolution organic light-emitting diode (OLED) displays. However, host materials used for MR-TADF emitters are mainly focused on small molecules that are relying on vacuum deposition for device fabrication. Here, we demonstrate the design of novel host materials with dendritic structures consisting of a non-conjugated adamantane core and four alkoxy-capped carbazole dendrons in periphery for solution-processed MR-TADF OLEDs with highly efficient narrowband electroluminescence. By introducing electron-donating n -butoxy capping groups to carbazole units and using the second-generation dendrons instead of the first-generation ones, triplet energies for the dendritic hosts are kept at higher than 2.80 eV, but the highest occupied molecular orbital (HOMO) levels can be considerably elevated from −5.51 to −5.19 eV, leading to barrier-free hole injection from anode to emissive layer. Solution-processed OLEDs based on the alkoxy-capped dendritic host and B,N-containing MR-TADF emitter reveal narrowband emission with full-width at half-maximum of 42 nm, together with low turn-on voltage of 2.8 V, maximum external quantum efficiency of 24.2% and power efficiency of 95.0 lm W−1, which represent the promising device efficiencies for narrowband electroluminescence by solution process. [ABSTRACT FROM AUTHOR]