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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]

Organic luminophores of narrowband emission are considered a filter-less light resource, promising for high-resolution organic light-emitting diode (OLED) display technology. It is essentially feasible to achieve narrowband emission by manipulating the intrinsic structural relaxation and vibronic coupling in the excited state. On this basis, by the introduction of single bond-linked peripheral moieties of 4-methoxyphenyl into the benzo[c]benzo [7,8]quinolino[1,2,3-fg]acridine-7,11-dione (BAO) core, the resulting BAO-PMO is observed to exhibit better performance, achieving a full width at half-maximum (FWHM) of down to 27 nm/0.14 eV in toluene for the narrowest band compared with that of BAO (35 nm/0.20 eV). An effective strategy is thus proposed by the significant enhancement of the low-frequency vibronic coupling strength with simultaneous mitigation of the high-frequency ones to realize the control of structural relaxation. In consequence, the BAO-PMO based OLED device exhibits a narrowband green emission with an FWHM of 37 nm/0.18 eV. • Organic narrowband luminophores based on carbonyl-bridged triarylamine were shown. • The emission narrowing was achieved via vibronic coupling regulation of the excited-state configuration. • Doped OLEDs exhibit narrowband green emission with a full width at half-maximum of down to 37 nm. [ABSTRACT FROM AUTHOR]

The ultra-high definition (UHD) displays in the market require organic light-emitting diodes (OLEDs) to meet the Rec.2020 color gamut standard, while it is still challenging to exploit ultra-deep-blue emitters that satisfy such blue standard. Herein, by substituting tCz (3,6-di(tert -butyl)carbazole) donor unit on the robust BOC (8,8,12,12-tetramethyl-8,12-dihydro-4-oxa-3a2-boradibenzo[ cd , mn ]pyrene) acceptor unit with high structural rigidity and appropriate energy levels, a novel boron-based D–A type thermally activated delayed fluorescence (TADF) ultra-deep-blue emitter, namely, tCz-BOC , was readily designed and synthesized. Inheriting from its rigid organoboron core, the emitter presents ultra-deep-blue emission with narrow spectral full width at half maximum (FWHM) of 54 nm and high photoluminescence quantum yield up to 73.7%. Additionally, tCz-BOC can effectively harvest T 1 excitons through high-lying T 2 mediated reverse intersystem crossing process. As a consequence, the fabricated OLED based on tCz-BOC exhibits a satisfactory ultra-deep-blue emission with λ EL of 424 nm, narrow emission bandwidth with FWHM of 47 nm, excellent maximum external quantum efficiency (EQE max) of 13.9%, as well as the CIE y coordinate of 0.047, which is fairly close to the Rec.2020 blue color gamut. A novel deep-blue thermally activated delayed fluorescence molecule. [Display omitted] • A robust TADF emitter tCz-BOC with ultra-deep-blue emission peaked at 428 nm and a narrow FWHM of 47 nm was obtained. • An excellent CIE y coordinate of 0.047 which is close to the Rec.2020 blue color gamut was achieved in its OLED. • The EQE max of the OLED was as high as 13.9%. [ABSTRACT FROM AUTHOR]

Multiple resonance thermally activated delayed fluorescence (MR-TADF) materials attract much attention owing to their 100 % exciton utilization, high photoluminescence quantum yield (PLQY) and narrowband emission with high color purity. However, how to regulate the energy levels and lifetimes of excited states for long-wavelength and short delayed fluorescence lifetime MR-TADF materials is still a challenge. Herein, an electron acceptor unit of pyrimidine derivative is introduced with steric-hinerance effect. The emission spectrum of BN-DPP is red shifted with 15 nm and the full width at half maximum (FWHM) is even narrower of 20 nm compared with that of DtCZB. A yellow-green MR-TADF material, called BN-DPBQ, is fabricated by extended the conjugation. Moreover, the delayed fluorescence lifetime of BN-DPBQ is half of that of BN-DPP. The BN-DPP based devices exhibit greenish blue emission with peak locating at 494 nm and maximum external quantum efficiency (EQE) of 23.6 %. BN-DPBQ based ones show much red shifted spectrum with emission peak at 538 nm and maximum EQE of 20.3 %. The results indicate that introducing electron acceptor units with steric-hinerance effect and extending the conjugation of resonance skeleton are effective ways to regulate energy levels and lifetimes of excited states for MR-TADF. [Display omitted] • Efficient energy levels and lifetimes regulation of excited states was proposed for narrowband TADF emitters. • BN-TPP was red-shifted of 15 nm with narrower FWHM by introducing electron acceptor with steric effect. • Red-shifted spectrum and decreased excited state lifetime were achieved by enlarging the conjugation of molecule. • BN-TPP and BN-DPBQ based devices demonstrated maximum EQEs of 24.3 and 22.8% with TADF or phosphorescent sensitizers. [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]

Multi-resonance emitters are attractive for organic light-emitting diode (OLED) applications because of their narrowband emissions and high photoluminescent efficiencies. Nevertheless, their tendency to aggregation by intermolecular interactions could cause doping sensitivity and reduce color purity at high concentrations. Here, we report a novel boron, sulfur (B, S)-containing multi-resonance emitter (BSS-Ph-TBCz) consisting of 1,8-diphenyl-carbazole substituent at para- position of boron atom of B, S-doped polycyclic aromatic skeleton. Different from control compound (BSS-TBCz) containing conventional carbazole substituents showing aggregation-caused spectral broadening, BSS-Ph-TBCz with 1,8-diphenyl-carbazole group exhibits weak intermolecular aggregation behavior owing to the large twist angle between polycyclic skeleton and carbazole plane caused by two steric phenyl groups on carbazole group, leading to nearly unchanged emissions with small full width at half-maximum of 30–31 nm at doping concentration ranging from 1 to 100 wt%. OLEDs employing BSS-Ph-TBCz as emitter reveal blue electroluminescence at 468 nm and maximum external quantum efficiency of 21.4% at 5 wt% doping concentration, which remains at 20.1% at high doping concentration of 25 wt%. [Display omitted] • Novel multi-resonance emitter with 1,8-diphenyl-carbazole substituent is developed. • Aggregation emission is suppressed by steric hindrance of 1,8-diphenyl-carbazole. • Rapid reverse intersystem crossing is realized by heavy-atom effect of sulfur. • EQE of >20% and FWHM of 31 nm are achieved for OLEDs at high doping concentration. [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]

Blue fluorescent emitters and devices are essential due to their unique advantages in realizing ultra-high-definition displays and reducing power consumption. Blue fluorescent emitters with narrow full width at half maximum (FWHM) emission spectra exhibit sufficient color purity to achieve ultra-high-definition displays with reduced power consumption. Much effort has been devoted to developing narrowband blue-emitting emitters and devices, and tremendous progress has been made over the past two decades. However, the reason for the narrowband emission of the emitters and the way to achieve the narrowband emission is unclear. Therefore, this work summarizes six types of emitters according to the reasons for inducing narrowband emission or/and the way to achieve narrowband emission and explores the relationship between the FWHM value of the emission spectrum of the emitter and the molecular structure or/and device structure. This work may inspire future researchers' enthusiasm for narrowband efficient blue emission research. This work summarizes six classes of emitters according to the reasons for inducing narrowband emission or/and the approach to achieving narrowband emission, obtains the relationship of emission spectrum FWHM to emitter structure, and demonstrates the approach to narrowband emission using advanced device technology. [Display omitted] • Six ways to realize narrowband emission are summarized. • Blue emitters and device technologies to achieve narrowband emission are summarized. • Design strategies for narrowband blue fluorescent emitters. [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]

At present, the investigation of luminescent materials with high color purity is becoming the hotspot domains, though red dyes and red solution-processed OLEDs are relatively scarce. Hence, three new BODIPY derivatives (BODIPYs) were designed and synthesized by modulating the energy gap (E g) and restricting rotation of substituents, namely B1 , B2 , and B3. Encouragingly, B1 , B2 , and B3 exhibited red narrowband emission in toluene, with the maximum emission peaks and full width at half maxima (FWHM) of 607, 615, 624 nm and 35, 41, 41 nm, respectively. And systematic studies demonstrated that introduction of sterically hindered tert -butyl and o-methoxybenzene units can not only restrict the rotation of substituents by means of changing the dihedral angle at the connection sites, but also regulate the energy gap (E g) by fine-tuning the frontier molecular orbitals. Ultimately, the PhCz-4CzTPN was employed as the dendritic TADF sensitizer, and the solution-processed OLEDs based on B3 exhibited standard pure red emission with an EQE max , an EL peak, a narrow FHWM, and Commission Internationale de l'Eclairage coordinates of 1.01%, 632 nm, 52 nm, and (0.67, 0.33), respectively. Fine-tuning the HOMO/LUMO of BODIPYs to achieve red emission while maintaining narrow-spectral emission, and the solution-proceed red TSF-OLEDs with high color purity were constructed based on BODIPYs, corresponding to an EQE max , an EL peak, a narrow FHWM, and CIE coordinates of 1.01%, 632 nm, 52 nm, and (0.67, 0.33), respectively. [Display omitted] • Three new narrow-spectrum red BODIPYs were obtained. • Introduction of substituents with steric hindrance can affect FWHM and energy gap. • Red TSF-OLEDs showed an FHWM of 52 nm and CIE coordinates of (0.67, 0.33). [ABSTRACT FROM AUTHOR]

Solar Thermophotovoltaics (STPV) has garnered great attention due to the pronounced energy transfer efficiency through a proper spectral transformation with respect to the bandgap of PV cells. In this work, we demonstrate a spectrally selective thermal emitter enabled by optical Tamm state (OTS) in a one-dimensional photonic structure, which is HfO 2 and SiO 2 layers alternatively stacked on a Mo substrate. The as-prepared emitter achieves a maximal simulated thermal emissivity up to 0.97, bandwidth down to 48 nm at 1.9 μm. The overall system efficiency of the proposed emitter-based STPV device is evaluated, which is up to 33.7% under the solar concentration of 2500 and area ratio of 20, providing a potential route towards the utilization of OTS-based emitters in practical STPV systems. • Easy-to-fabricate 1D emitter based on optical Tamm state (OTS). • Simulated emission spectrum with a maximal emissivity up to 0.97 and a minimal linewidth of 48 nm at the resonant wavelength. • 8% promotion of the calculated system-level efficiency of the OTS emitter compared to the CPA emitter. [ABSTRACT FROM AUTHOR]

[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]