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The research on boron/nitrogen (B/N)-based multiresonance thermally activated delayed fluorescence (MR-TADF) emitters has been a prominent topic due to their narrowband emission and high luminous efficiency. However, devices derived from the common types of narrowband TADF materials often experience an efficiency roll-off, which could be ascribed to their relatively slow triplet–singlet exciton interconversion. Since inserting the heavy Se atom into the B/N scheme has been a proven strategy to address the abovementioned issues, herein, extensive density functional theory (DFT) and time-dependent DFT (TD-DFT) simulations have been employed to explore the effects of the structural modification on a series of structurally modified selenium-doped derivatives. Furthermore, the two-layered ONIOM (QM/MM) model has been employed to study the pressure effects on the crystal structure and photophysical properties of the pristine CzBSe. The theoretical results found that the introduced tert-butyl units in Cz-BSeN could result in a shorter charge transfer distance and smaller reorganization energy than the parent CzBSe. In contrast to directly incorporating the o-carborane (Cb) unit to CzBSe, incorporating the bridged phenyl units is important in order to achieve narrowband emissions and high luminous efficiency. The lowest three triplet excited states of CzBSe, Cz-BSeN and PhCb-BSeN all contribute to their triplet–singlet exciton conversions, resulting in a high utilization of triplet excitons. The pressure has an evident influence on the photophysical properties of the aggregated CzBSe and is favored for obtaining narrowband emissions. Our work is promised to provide a feasible strategy for designing selenium-doped derivatives with narrowband emissions and rapid triplet–singlet exciton interconversions. [ABSTRACT FROM AUTHOR]

The development of red phosphors with good thermal stability, high quantum yield and high color purity is still a big challenge. In this work, a series of novel red phosphors Sr3La2W2O12:xEu3+ (0≤x≤0.18, ∆x = 0.03) were successfully prepared by high‐temperature solid‐phase method. The phosphors reveal a hexagonal phase with the space group of R‐3 m. The phosphor Sr3La2W2O12:Eu3+ produced narrowband red emission from 5D0→7F2 of Eu3+ (616 nm) under excitation at 395 nm, 465 nm, and 533 nm. Importantly, phosphor Sr3La2W2O12:0.09Eu3+ exhibits astonishing quantum efficiency (IQE = 89.60%, EQE = 41.52%), and it demonstrate robust thermal performance with the emission intensity retaining 92.73% at 558 K of that at 298 K. Finally, the prepared red phosphor Sr3La2W2O12:0.09Eu3+ and yellow phosphor YAG:Ce3+ were combined with a blue LED chip (460 nm) to form a WLED device, which presented warm white light with color coordinates of (0.3523, 0.3732), color rendering index of 83.7, and color temperature of 4826 K. [ABSTRACT FROM AUTHOR]

Thermally activated delayed fluorescence (TADF) materials with high photoluminescence quantum yields and fast reverse intersystem crossing (RISC) capabilities are highly desirable for applications in high-efficiency organic light-emitting diodes. Herein, we report the synthesis as well as structural and photophysical properties of 5,9-diselena-13b-boranaphtho [3,2,1-de]anthracene (SeBSe) as a narrowband-emissive TADF material. The incorporation of two selenium atoms into the boron-fused pentacyclic π-core results in a small singlet-triplet energy gap (Δ£^) and thereby significant TADF properties. Moreover, theoretical calculations revealed a noticeable spin-orbit coupling enhancement between the singlet and triplet manifolds in SeBSe by virtue of the heavy-atom effect of selenium atoms. Consequently, SeBSe allows ultrafast spin-flip RISC with the rate constant surpassing 108 s-1, which far exceeds the corresponding fluorescence radiative decay rate (~106 s-1), enabling an ideal singlet-triplet superimposed excited state. [ABSTRACT FROM AUTHOR]

The research on boron/nitrogen (B/N)-based multiresonance thermally activated delayed fluorescence (MR-TADF) emitters has been a prominent topic due to their narrowband emission and high luminous efficiency. However, devices derived from the common types of narrowband TADF materials often experience an efficiency roll-off, which could be ascribed to their relatively slow triplet–singlet exciton interconversion. Since inserting the heavy Se atom into the B/N scheme has been a proven strategy to address the abovementioned issues, herein, extensive density functional theory (DFT) and time-dependent DFT (TD-DFT) simulations have been employed to explore the effects of the structural modification on a series of structurally modified selenium-doped derivatives. Furthermore, the two-layered ONIOM (QM/MM) model has been employed to study the pressure effects on the crystal structure and photophysical properties of the pristine CzBSe. The theoretical results found that the introduced tert-butyl units in Cz-BSeN could result in a shorter charge transfer distance and smaller reorganization energy than the parent CzBSe. In contrast to directly incorporating the o-carborane (Cb) unit to CzBSe, incorporating the bridged phenyl units is important in order to achieve narrowband emissions and high luminous efficiency. The lowest three triplet excited states of CzBSe, Cz-BSeN and PhCb-BSeN all contribute to their triplet–singlet exciton conversions, resulting in a high utilization of triplet excitons. The pressure has an evident influence on the photophysical properties of the aggregated CzBSe and is favored for obtaining narrowband emissions. Our work is promised to provide a feasible strategy for designing selenium-doped derivatives with narrowband emissions and rapid triplet–singlet exciton interconversions.

Thermally activated delayed fluorescence (TADF) materials with high photoluminescence quantum yields and fast reverse intersystem crossing (RISC) capabilities are highly desirable for applications in high-efficiency organic light-emitting diodes. Herein, we report the synthesis as well as structural and photophysical properties of 5,9-diselena-13b-boranaphtho[3,2,1-de]anthracene (SeBSe) as a narrowband-emissive TADF material. The incorporation of two selenium atoms into the boron-fused pentacyclic π-core results in a small singlet–triplet energy gap (ΔEST) and thereby significant TADF properties. Moreover, theoretical calculations revealed a noticeable spin-orbit coupling enhancement between the singlet and triplet manifolds in SeBSe by virtue of the heavy-atom effect of selenium atoms. Consequently, SeBSe allows ultrafast spin-flip RISC with the rate constant surpassing 108 s−1, which far exceeds the corresponding fluorescence radiative decay rate (∼106 s−1), enabling an ideal singlet–triplet superimposed excited state.

Multiple resonance (MR) emitters are promising for the next-generation wide color gamut organic light-emitting diodes (OLEDs) with narrowband emissions; however, they still face intractable challenges such as concentration-induced emission quenching, exciton annihilation, and spectral broadening. In this concept, we focus on an advanced molecular design strategy called “sterically wrapping of MR fluorophores” to address the above issues. By isolating the MR emission core using bulky substituents, intermolecular interactions can be significantly suppressed to eliminate the formation of unfavorable species. Consequently, using the newly designed emitters, optimized MR-OLEDs can achieve high external quantum efficiencies of >40% while maintaining extremely small full width at half maxima (FWHMs) of

Ultra‐narrowband blue multi‐resonance‐induced thermally activated delayed fluorescence (MR‐TADF) materials (V‐DABNA and V‐DABNA‐F), consisting of three DABNA subunits possessing phenyl or 2,6‐difluorophenyl substituents on the peripheral nitrogen atoms are synthesized by one‐shot triple borylation. Benefiting from the inductive effect of fluorine atoms, the emission maximum of V‐DABNA‐F (464 nm) is blueshifted from that of the parent V‐DABNA (481 nm), while maintaining a small full width at half maximum (FWHM, 16 nm) and a high rate constant for reverse intersystem crossing (6.5 × 105 s−1). The organic light‐emitting diodes (OLEDs) using V‐DABNA and V‐DABNA‐F as emitters are fabricated by vapor deposition and exhibit blue emission at 483 and 468 nm with small FWHMs of 17 and 15 nm, corresponding to Commission Internationale d'Éclairage coordinates of (0.09, 0.27) and (0.12, 0.10), respectively. Both devices achieve high external quantum efficiencies of 26.2% and 26.6% at the maximum with minimum efficiency roll‐offs of 0.9% and 3.2%, respectively, even at 1000 cd m−2, which are record‐setting values for blue MR‐TADF OLEDs. [ABSTRACT FROM AUTHOR]

Abstract Ultra‐narrowband blue multi‐resonance‐induced thermally activated delayed fluorescence (MR‐TADF) materials (V‐DABNA and V‐DABNA‐F), consisting of three DABNA subunits possessing phenyl or 2,6‐difluorophenyl substituents on the peripheral nitrogen atoms are synthesized by one‐shot triple borylation. Benefiting from the inductive effect of fluorine atoms, the emission maximum of V‐DABNA‐F (464 nm) is blueshifted from that of the parent V‐DABNA (481 nm), while maintaining a small full width at half maximum (FWHM, 16 nm) and a high rate constant for reverse intersystem crossing (6.5 × 105 s−1). The organic light‐emitting diodes (OLEDs) using V‐DABNA and V‐DABNA‐F as emitters are fabricated by vapor deposition and exhibit blue emission at 483 and 468 nm with small FWHMs of 17 and 15 nm, corresponding to Commission Internationale d’Éclairage coordinates of (0.09, 0.27) and (0.12, 0.10), respectively. Both devices achieve high external quantum efficiencies of 26.2% and 26.6% at the maximum with minimum efficiency roll‐offs of 0.9% and 3.2%, respectively, even at 1000 cd m−2, which are record‐setting values for blue MR‐TADF OLEDs.

The generation of monochromatic electromagnetic radiation in the terahertz (THz) frequency range has remained a challenging task for many decades. Here, the emission of monochromatic sub-THz radiation by optical phonons in the dielectric material KY(MoO 4 ) 2 is demonstrated. The layered crystal structure of KY(MoO 4 ) 2 causes infrared-active shear lattice vibrations to have energies below 3.7 meV, corresponding to frequencies lower than 900 GHz where solid-state-based monochromatic radiation sources are rare. Directly excited by a 5 ps long broadband THz pulse, infrared-active optical vibrations in KY(MoO 4 ) 2 re-emit narrowband sub-THz radiation as a time-varying dipole for tens of picoseconds, which is exceptionally long for oscillators with frequencies below 1 THz. Such a long coherent emission allows for the detection of more than 50 periods of radiation with frequencies of 568 and 860 GHz. The remarkably long decay time together with the chemical stability of the employed material suggests a variety of possible applications in THz technology., (© 2024 The Author(s). Advanced Science published by Wiley‐VCH GmbH.)

A unique molecular design paradigm aimed at developing solution-processed multiple resonance-induced thermally activated delayed fluorescence (MR-TADF) materials is proposed here, the solution processing ability could be enhanced by integrating three MR-building blocks. When utilized as an emitter in solution-processed organic light-emitting diodes (sOLEDs), the synthesized TriBNCz molecule demonstrates a narrow emission spectrum with full width at half maximum (FWHM) of 27 nm. Furthermore, through a sensitization strategy, the sOLED device achieves impressive maximum external quantum efficiency (EQE) of 28.8 % and maintains 26.1 % at 1000cd/m−2, with an FWHM of 30 nm and Commission Internationale de I'Éclairage (CIE) coordinates of (0.103, 0.497). [Display omitted] • A novel narrowband multiple resonance delayed fluorescence emitter is developed through the integration of MR-building blocks; • A higher k RISC has been achieved owing to the mixed SRCT and LRCT characteristic of excited states as well as multiple charge transfer channels; • Quite high maximum EQE of 28.8 % and a high-level EQE of 26.1 % at 1000 cd/m2, with an FWHM of 30 nm have been realized. Solution-processed organic materials that exhibit both high emission efficiency and narrowband emission characteristics are rare, and the performance of corresponding solution-processed organic light-emitting diodes (sOLEDs) remains inadequate for practical applications. This study proposes a proof-of-concept design aimed at enhancing both solution processing capability and emission efficiency in multiple-resonance induced thermally activated delayed fluorescence (MR-TADF) materials through the integration of multiple emitting units. A unique emitter named TriBNCz is synthesized and characterized, incorporating three MR-building blocks onto a single phenyl ring, resulting in sky-blue emission with a peak at 490 nm and a small full width at half maximum (FWHM) of 25 nm. Significant improvements in solution processing attributes, including solubility and film-forming properties, are achieved. Moreover, except for the MR effect of the excited states, long-range charge transfer properties of excited states are also obtained. The multiple charge transfer channels contribute to higher rate of reverse intersystem crossing (k RISC). The optimized sOLED device exhibits a maximum external quantum efficiency (EQE max) of 17.8 %. Furthermore, by employing 5TCzBN as a sensitizer, the sensitized sOLED achieves an EQE max of 28.8 % and a high-level EQE of 26.1 % at 1000 cd m−2, with an FWHM of 30 nm and Commission Internationale de I'Éclairage (CIE) coordinates of (0.103, 0.497), representing one of the best results among narrowband emission sOLEDs. This research opens a new avenue to develop high-performance solution-processed organic materials and sOLED devices. [ABSTRACT FROM AUTHOR]

[Display omitted] • PYHB and PYHP deliver excellent thermal stability and morphological stability. • PYHB and PYHP can inherit the narrowband blue emission and HLCT characteristics. • PYHB and PYHP remove the limitations of traditional polymer luminescent materials. • PYHB and PYHP outperform previously reported polymer luminescent materials. • Our strategy provides a promising platform for PIs as a photoelectric material. Blue light-emitting materials with excellent film-forming ability, superior morphological stability, outstanding color purity, and high device efficiency are in urgent demand for new-generation display and solid-state lighting devices fabricated by low-cost wet processing. However, their current performances are far from satisfactory. Herein, two polyimide (PI)-based blue polymers are first precisely constructed and synthesized through a "Hinge-type Linking" strategy. A small molecular is introduced into the PI backbone via non-conjugated aliphatic imide ring linker. These polymers not only show superb thermal stability and morphological stability, but also maintain narrowband blue emission. Furthermore, PIs are prepared by polycondensation method, precipitated and purified in ethanol solvent, which avoids the use of metal catalysts. The resulting solution-processable devices achieve high performance with a maximum external quantum efficiency (EQE) of 9.94 % and maximum emission peak at 460 nm. To the best of our knowledge, this is the first time that solution-processable polymer light-emitting diodes (PLEDs) based on the "hot exciton" mechanism achieving splendid performance with maximum EQE close to 10 %. The superior performance is attributed to the validity of the "Hinge-type Linking" strategy in PLEDs, opening up a new avenue for PLED development and application. [ABSTRACT FROM AUTHOR]

Abstract CsPbX 3 perovskite nanocrystals (NCs) are still limited in their use due to their extreme instability in the air as they will deteriorate in a few days, and their thermal stability is not optimistic. In this study, the red CsPbBr x I 3-x (X = 1.5, 1.0, 0.8, 0.5, 0.35, 0) NCs and Mn-doped CsPbBr x I 3-x NC in zinc borosilicate (B 2 O 3 -SiO 2 -ZnO) glass with cubic perovskite crystal structure were successfully synthesized through melt-quenching and heat-treatment method, which exhibited strong red emission in region of 572 nm–708 nm under 365 nm excitation. Additionally they are stable in the air for several months while showing excellent thermal stability. It is worth mentioning that Mn-doped CsPbBr x I 3-x NC glasses are brighter than CsPbBr x I 3-x NC glasses under UV light. Because Mn-doped CsPbBr x I 3-x NC glasses have good thermal and air stability, they can be used as a red fluorescent material. We fabricated glass with Y 3 Al 5 O 12 :Ce3+ (YAG:Ce3+) phosphor-in-glass (PiG) realized the chromaticity tuning for YAG:Ce3+ phosphor with white light-emitting-diodes (WLED). Highlights • Mn-doped CsPbBr x I 3-x NC glass with a strong red fluorescence. • The glass maintains the cubic perovskite crystal structure like NCs. • By changing the ratio of halogen, the emission band was tuned from 572 nm to 708 nm. • The glass overcomes the air instability and poor water resistant properties. • The glass can used as red phosphor and stacked on the Ce-PiG to achieve warm WLED. [ABSTRACT FROM AUTHOR]

Boron, sulfur-doped polycyclic aromatic hydrocarbon emitters with multiple-resonance-dominated lowest excited states are developed by tuning energy level alignment between 5,9-dithia-13b-boranaphtho[3,2,1- de ]anthracene skeleton and peripheral arylamine moieties, which reveal narrowband deep-blue electroluminescence with full-width at half maximum of 29 nm, Commission Internationale de l'Éclairage color coordinates of (0.13, 0.09) and maximum external quantum efficiency of 21.8%. [Display omitted] • Novel B,S-doped polycyclic aromatic multiple resonance emitters are developed. • Sulfur atoms enhance spin-orbital coupling and reverse intersystem crossing. • The lowest excited state characteristics are regulated by arylamine substituents. • The emitters exhibit narrowband deep-blue electroluminecence with EQE of 21.8%. Different from boron, nitrogen-based multiple resonance thermally activated delayed fluorescence (MR-TADF) emitters, boron (B), sulfur (S)-doped polycyclic aromatic hydrocarbons (PAHs) containing 5,9-dithia-13b-boranaphtho[3,2,1- de ]anthracene (BSS) skeleton and arylamine moieties in para -positions of boron atoms are developed as a novel kind of MR-TADF emitters for narrowband deep-blue electroluminescence. The molecular design not only utilizes heavy-atom effect of sulfur atoms in BSS skeleton to enhance spin-orbital coupling and promote reverse intersystem crossing, but also uses arylamines as peripheral substituents to modify excited state characteristics. By decreasing electron-donating ability and downshifting HOMO level of arylamines, the lowest excited state for resultant emitter is converted from intersegmental charge transfer state to multiple resonance state localized on BSS skeleton, leading to blue-shifted and narrowed emissions. The B,S-doped PAH emitter bearing carbazole moiety exhibits deep-blue electroluminecence with full-width at half maximum of 29 nm, Commission Internationale de l'Éclairage color coordinates of (0.13, 0.09), and the maximum external quantum efficiency of 21.8 %, representing a new approach toward efficient narrowband deep-blue emission beyond boron, nitrogen-based MR-TADF emitters. [ABSTRACT FROM AUTHOR]

[Display omitted] • Deep Blue MR-TADF emitters were designed by incorporating rigid DOBNA into MR skeletons. • Both emitters possess narrowband deep blue emission with FWHM of 19 nm. • Small ΔE ST (0.05 eV) and high PLQY are realized in the emitters. • MR-TADF OLEDs demonstrate high EQEs (>30 %) with CIE y coordinate below ≤ 0.07. The simultaneous achievement of high efficiency and deep blue narrowband emission in multi resonant thermally activated delayed fluorescence (MR-TADF) materials are crucial and challenging. Herein we report two deep blue MR-TADF emitters, namely, TPD4PA and tBu-TPD4PA , using double boron, three nitrogen and two oxygen atoms. The design is based on amalgamating the high charge transfer (CT) characteristic moiety into MR-type fragments towards efficient MR-TADF emitters with improved CT characteristics. Both the materials show deep blue photo luminescent emissions of ∼450 nm with a high photoluminescence quantum yield (PLQY) of ∼90 %. These materials showed very small singlet–triplet gap (≤0.06 eV) and a high rate of reverse intersystem crossing of ∼2.5 × 105 s−1. The TADF devices based on TPD4PA and tBu-TPD4PA showed maximum external quantum efficiencies of 30.7 and 32.5 %, respectively. Furthermore, both devices exhibited narrow band deep blue emissions and corresponding CIE y coordinates 0.06 and 0.07, which match near NTSC and BT2020 blue color requirements. [ABSTRACT FROM AUTHOR]

Multiple resonance (MR) emitters are promising for the next-generation wide color gamut organic light-emitting diodes (OLEDs) with narrowband emissions; however, they still face intractable challenges such as concentration-induced emission quenching, exciton annihilation, and spectral broadening. In this concept, we focus on an advanced molecular design strategy called "sterically wrapping of MR fluorophores" to address the above issues. By isolating the MR emission core using bulky substituents, intermolecular interactions can be significantly suppressed to eliminate the formation of unfavorable species. Consequently, using the newly designed emitters, optimized MR-OLEDs can achieve high external quantum efficiencies of >40% while maintaining extremely small full width at half maxima (FWHMs) of <25 nm over a wide range of concentrations (1-20 wt%). This strategy may shed light on the design of efficient MR emitters, which provides more room for tuning the dopant concentrations under the premise of high-efficiencies and small FWHMs, accelerating the practical application of MR-OLEDs., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Xiaofeng, Dongdong, Lian and Yuewei.)

[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]

Ultra-narrowband blue multi-resonance-induced thermally activated delayed fluorescence (MR-TADF) materials (V-DABNA and V-DABNA-F), consisting of three DABNA subunits possessing phenyl or 2,6-difluorophenyl substituents on the peripheral nitrogen atoms are synthesized by one-shot triple borylation. Benefiting from the inductive effect of fluorine atoms, the emission maximum of V-DABNA-F (464 nm) is blueshifted from that of the parent V-DABNA (481 nm), while maintaining a small full width at half maximum (FWHM, 16 nm) and a high rate constant for reverse intersystem crossing (6.5 × 10 5 s -1 ). The organic light-emitting diodes (OLEDs) using V-DABNA and V-DABNA-F as emitters are fabricated by vapor deposition and exhibit blue emission at 483 and 468 nm with small FWHMs of 17 and 15 nm, corresponding to Commission Internationale d'Éclairage coordinates of (0.09, 0.27) and (0.12, 0.10), respectively. Both devices achieve high external quantum efficiencies of 26.2% and 26.6% at the maximum with minimum efficiency roll-offs of 0.9% and 3.2%, respectively, even at 1000 cd m -2 , which are record-setting values for blue MR-TADF OLEDs., (© 2022 The Authors. Advanced Science published by Wiley-VCH GmbH.)

[Display omitted] • Newly synthesized diboron embedded deep blue MR-TADF emitters. • Narrow spectra with FWHM of 14 nm and CIE y coordinate below 0.10. • Small △E ST (≤0.07 eV), high PLQY, and good TADF performances. • All these materials show high EQEs (>33%) We report three deep blue multiple resonant TADF emitters, m-ν-DABNA, 4F-ν-DABNA, and 4F-m-ν-DABNA by incorporating methyl groups and fluorine atoms in diboron based ν-DABNA core. The introduction of methyl groups at para positions to the boron atoms and fluorine atoms at ortho positions to the nitrogen atoms resulted in bandgap enhancement by electron donating and electron withdawing effects. All three emitters exhibit pure blue emissions with high photoluminescence quantum yield around ∼ 90%, small ΔE ST (≤0.07 eV) values, and fast reverse intersystem crossing rate (k RISC). Fabricated OLEDs with these emitters show excellent external quantum efficiency over 33%. Among three materials, 4F-ν-DABNA and 4F-m-ν-DABNA exhibit the CIE y coordinate of 0.08 and 0.06, respectively. Our current material design approach guides a path for the development of deep blue TADF emitters for highly efficient narrowband OLEDs. [ABSTRACT FROM AUTHOR]