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Ultranarrow Deep-Blue Luminescence of Perovskite Nanocrystals by A-Site Cation Control.

Metal-halide perovskite nanocrystals (NCs) are one of the most promising emitters for the application of display and nanolight sources. The full width at half-maximum (FWHM) of photoluminescence (PL) emission is essential for color purity, which however remains a difficulty to further reduce the FWHM of the perovskite NCs at room temperature. Here, we show the quasi-sphere perovskite NCs with narrow PL emission at a deep-blue wavelength of ∼430 nm; its PL FWHM reaches ∼11 nm at room temperature, owing to the monodispersion in size distribution as well as the symmetric quasi-sphere morphology of NCs releasing the fine structure splitting-induced inhomogeneous broadening. Through regulating A cations with respect to the ratio of FA (or MA)-to-Cs and Cs-to-Pb, the PL emission of the NCs could be tuned from ∼505 to ∼430 nm combined with varied morphologies from large cube to small quasi-sphere. Such spectroscopic and morphological discrepancies are supposed to be attributed to the different crystalline kinetics that is strongly dependent on the synthetic condition. To be specific, in the case of increasing FA (or MA)-to-Cs, the growth rate of CsPbBr3 and FAPbBr3 (or MAPbBr3) perovskites is determined by the reactivity of transient species, while in the case of decreasing the Cs-to-Pb ratio, the growth rate of perovskites is slowed down by the serious reduction of Cs+ in the precursor. This study provides an effective strategy to adjust the emission across from green to deep-blue color and promotes the perovskite NCs with a narrow FWHM, and tunable PL emission facilitates in application of optoelectronic devices.

Robust Radicals Featuring B- and N-Embedded Dioxygen-Bridged Units: Synthesis, Structures, and Optical Properties.

Tris(2,4,6-trichlorophenyl)methyl (TTM) group has been widely used for constructing organic radicals, but the poor optical stabilities limit the application prospects of the TTM radicals. In this work, the rigid B- and N-embedded dioxygen-bridged (BO and NO) units were attached to the TTM skeleton as the strong electron-withdrawing and electron-donating groups, respectively. The rigidity and strong electronic effect of the BO and NO units contribute to the high chemical and optical stability of BO-TTM and NO-TTM radicals. Notably, NO-TTM exhibits near-infrared emission at 830 nm with a narrow full width at half maximum (FWHM) of 55 nm (100 meV), while BO-TTM shows blue-shifted luminescence at 635 nm and a narrower FWHM of merely 43 nm (130 meV). This study has developed a methodology to produce highly efficient and enduring luminescent radicals, which could tune emission properties such as wavelength and FWHM.

Stepwise Toward Pure Blue Organic Light-Emitting Diodes by Synergetically Locking and Shielding Carbonyl/Nitrogen-Based MR-TADF Emitters.

Deep-blue multi-resonance (MR) emitters with stable and narrow full-width-at-half-maximum (FWHM) are of great importance for widening the color gamut of organic light-emitting diodes (OLEDs). However, most planar MR emitters are vulnerable to intermolecular interactions from both the host and guest, causing spectral broadening and exciton quenching in thin films. Their emission in the solid state is environmentally sensitive, and the color purity is often inferior to that in solutions. Herein, a molecular design strategy is presented that simultaneously narrows the FWHM and suppresses intermolecular interactions by combining intramolecular locking and peripheral shielding within a carbonyl/nitrogen-based MR core. Intramolecularly locking carbonyl/nitrogen-based bears narrower emission of 2,10-dimethyl-12,12-diphenyl-4H-benzo[9,1]quinolizino[3,4,5,6,7-defg]acridine-4,8(12H)-dione in solution and further with peripheral-shielding groups, deep-blue emitter (12,12-diphenyl-2,10-bis(9-phenyl-9H-fluoren-9-yl)-4H-benzo[9,1]quinolizino[3,4,5,6,7-defg]acridine-4,8(12H)-dione, DPQAO-F) exhibits ultra-pure emission with narrow FWHM (c.a., 24nm) with minimal variations (∆FWHM ≤ 3nm) from solution to thin films over a wide doping range. An OLED based onDPQAO-F presents a maximum external quantum efficiency (EQEmax) of 19.9% and color index of (0.134, 0.118). Furthermore, the hyper-device of DPQAO-F exhibits a record-high EQEmax of 32.7% in the deep-blue region, representing the first example of carbonyl/nitrogen-based OLED that can concurrently achieve narrow bandwidth in the deep-blue region and a high electroluminescent efficiency surpassing 30%.

Sodium-based no-core fiber surface plasmon resonance sensor with high sensitivity and narrow FWHM

Since fiber-optic sensors using noble metal-excited surface plasmon resonance (SPR) effects have encountered bottlenecks in improving performance, we propose a fiber-optic sensor using sodium in combination with a no-core fiber (NCF) to measure both refractive index (RI) and temperature. We deposited sodium thin films on the surface of NCF optical fibers and protected them with polymethyl methacrylate (PMMA) or polydimethylsiloxane (PDMS) for RI sensing or temperature sensing. We performed computational simulations and performance analyses of the sensors using the finite element method, and the results show that the sodium-based SPR sensors have higher sensitivity, wider detection range, and narrower full width at half-maximum (FWHM) than the noble metal SPR sensors. SPR sensors with different sodium film thicknesses have different sensing characteristics, so we can get optical fiber sensors with more flexible transmission characteristics, which helps us arrange sensors more conveniently in practical applications. The simulation and numerical results show that when the sensor is used to measure RI, the average sensitivity of the sensor can reach 7977 nm RIU−1, the maximum sensitivity can reach 23100 nm RIU−1, the narrowest FWHM is 14.23 nm, and the maximum figure of merit (FOM) is 719.42 RIU−1 under different thicknesses of sodium film. The corresponding RI ranges from 1.32 to 1.41. When the temperature measurement range is 0 °C ∼ 100 °C, the average sensitivity can reach 7.86 nm °C−1, the maximum temperature sensitivity can reach 21.1 nm °C−1, and the narrowest FWHM is 17.84 nm. In summary, the proposed sodium-based SPR sensor has flexible and high-performance sensing characteristics, and our research work provides more powerful theoretical support for the application of sodium-based plasma devices.

Single crystal growth of complex layered oxychalcogenide by melt-solidification method

We have successfully grown single crystals of layered mixed-anion compound Sr2ZnCu2Se2O2 by a simple melt-growth method. Single crystals of the layered oxychalcogenides Sr2ZnCu2Se2O2 were grown by melt-solidification of stoichiometric raw materials. Plate-like single crystals were obtained, and the maximum size of crystals was 2.5 × 1.4 mm2. Thermal analysis result indicates simple melting-solidification-like behavior, and the size of crystals increases significantly above the melting point revealed by this measurement. X-ray rocking curve (XRC) measurement results of the single crystal showed no peak splitting, with a narrow full width half maximum of 30 and 97 arcsec in (105) and (0012) peaks, respectively. The electrical conductivity of single crystals on the a(b) plane was 4.34 × 10−1 S/cm at room temperature. Obtained single crystals were transparent, and the absorption edge was observed around 560 nm in the transmittance measurement. Although layered oxychalcogenide Sr2ZnCu2Se2O2 has a complex composition and structure, this compound exhibits congruent melting behavior in a sealed environment. This feature enables us to grow single crystals of mixed-anion compounds easily by the melt-growth method.

High-efficiency top-emitting organic light-emitting diodes based on metal/ITO composite electrodes

High-performance top-emitting organic light-emitting diodes (TEOLEDs) integrating the metal/ITO composite anodes were developed. The results revealed that covering the surface of Al anode with ITO layer could effectively improve the charge injection efficiency and balance the hole–electron charge. The effect of the thickness of ITO on the performance of TEOLEDs with Al/ITO anodes was further studied. The TEOLEDs with Al/ITO (5 nm) anode showed optimized performance, with the current efficiency (CE) and external quantum efficiency (EQE) enhanced by 40.0% and 34.5% compared to that of the OELD with pure Al anode, and increased by 93.1% and 33.5% compared to that of bottom-emitting OLEDs. In addition, the full width at half maximum (FWHM) was narrowed to 36 nm due to the micro-cavity effect of the top-emitting structure and the turn-on voltage decreased to as low as 2.3 V owing to the efficient charge injection and well-matched energy level. In addition, TEOLEDs using Ag/ITO as anode exhibited a slow roll-off of CE and EQE and a narrower FWHM of 30 nm, greatly improving the color purity. The strategy is simple and can significantly improve the efficiency of the TEOLEDs, which promotes the applications of OLEDs in the fields of ultra-high-definition displays and micro-displays.

Efficient narrowband yellow organic light-emitting diodes based on iridium(III) complexes with the rigid indolo[3,2,1-jk]carbazole unit.

Phosphorescent material with narrowband emission is crucial for advancing wide-color-gamut organic light-emitting diodes (OLEDs). In this work, two iridium(III) complexes, (PhthzICz)2Ir(tmd) and (thzICz)2Ir(tmd), using rigid 2-(benzothiazole-2-yl)indolo[3,2,1-jk]carbazole (PhthzICz) and 2-(thiazole-2-yl)indolo[3,2,1-jk]carbazole (thzICz) as cyclometalated ligands and 2,2,6,6-tetramethyl-3,5-heptanedione (tmd) as ancillary ligands, were synthesized. When these complexes were doped into the host material 3,3'-di(9H-carbazol-9-yl)-1,1'-biphenyl, the doped films exhibited yellow photoluminescence (PL) peaking at 537 and 531 nm, full width at half maximum (FWHM) bands of 35 and 60 nm, and PL quantum yields of 89.9% and 85.9%, respectively. OLEDs based on these two emitters display moderate performance characteristics with maximum external quantum efficiencies of 25.2% and 22.7%. Notably, the device based on (PhthzICz)2Ir(tmd) exhibits a narrow FWHM of 31 nm. Overall, the study highlights the practicality of incorporating rigid groups into the cyclometalated ligands of Ir(III) complexes as a viable strategy for achieving efficient Ir(III) complexes for OLEDs with narrow emission and high efficiency.

Interference filter based external-cavity diode laser with combined dual interference filters and largely adjustable feedback range

External-cavity diode lasers (ECDL) are widely used as light sources in laser spectroscopy, atomic physics, and quantum optics. This study demonstrated a home-made 852–nm ECDL with variable feedback, using the combined dual narrow-band interference filters (IFs) as the laser longitudinal mode selection element. The combination of narrow-band IFs, mainly for the current commercially available narrow-band IFs with the full width at half maximum (FWHM) of approximately 0.5 nm for 780-895 nm. We designed different narrow-band IFs combinations to achieve a narrower FWHM, and applied them in the ECDL. The combination of the dual narrow-band IFs further reduces the laser linewidth. We measured the laser linewidth using a high-finesse Fabry-Perot cavity with a linewidth of approximately 10 kHz. The laser linewidth is approximately 176 kHz for the Single-IF-ECDL and 96 kHz for the Dual-IF-ECDL with the same feedback. In addition, we have experimentally verified the results of narrower laser linewidth and larger tuning range with increase in the feedback. The developed Dual-IF-ECDL has the capability of narrow linewidth and wavelength tunability and can be applied to precision spectroscopy, cooling and trapping of neutral atoms.

Solid superacid catalysts promote high-performance carbon dots with narrow-band fluorescence emission for luminescence solar concentrators

Facile and efficient method for constructing carbon dots (CDs) with narrow full width at half maximum (FWHM) is a major challenge in the field, and researches on regulating the FWHM of CDs are also rare and scarce. In this work, we delved into the synthesis of CDs with narrow fluorescence emission FWHM (NFEF-CDs) in the m-phenylenediamine (m-PD)/ethanol system, utilizing solid superacid resin as catalyst with solvothermal method. The resulting NFEF-CDs exhibit a photoluminescent (PL) emission peak at 521 nm with a narrow FWHM of 41 nm, an absolute PL quantum yield (QY) of 80%, and display excitation-independent PL behavior. Through comprehensive characterization, we identified the protonation of edge amino on NFEF-CDs as the key factor in achieving the narrow FWHM. Subsequently, we validated the broad applicability of solid superacid resins as catalysts for synthesizing CDs with narrow FWHM in the m-PD/ethanol system. Finally, we utilized a self-leveling method to prepare NFEF-CDs film on the surface of poly(methyl methacrylate) (PMMA) substrate and investigated the solid-state fluorescence properties of NFEF-CDs as well as their performance as luminescence solar concentrator (LSC) for photovoltaic conversion. The results revealed that the as-prepared LSC exhibit an internal quantum efficiency (ηint) of 42.39% and an optical efficiency (ηopt) of 0.68%. These findings demonstrate the promising prospects of NFEF-CDs in the field of LSCs and provide a theoretical basis for their application in photovoltaic conversion.

Enhanced Near-Infrared Ultra-Narrow Absorber Based on a Dielectric Nano-Resonant Ring for Refractive Index Sensing.

In this paper, a plasmon resonance-enhanced narrow-band absorber based on the nano-resonant ring array of transparent conductive oxides (TCOs) is proposed and verified numerically. Due to the unique properties of TCOs, the structure achieves an ultra-narrowband perfect absorption by exhibiting a near-field enhancement effect. Consequently, we achieve a peak absorption rate of 99.94% at 792.2 nm. The simulation results indicate that the Full Width Half Maximum (FWHM) can be limited to within 8.8 nm. As a refractive index sensor, the device reaches a sensitivity S of 300 nm/RIU and a Figure of Merit (FOM) value of 34.1 1/RIU. By analyzing the distribution characteristics of the electromagnetic field at the 792.2 nm, we find high absorption with a narrow FWHM of the ITO nano-resonant ring (INRR) owing to plasmon resonance excited by the free carriers at the interface between the metal and the interior of the ITO. Additionally, the device exhibits polarization independence and maintains absorption rates above 90% even when the incident formed by the axis perpendicular to the film is greater than 13°. This study opens a new prospective channel for research into TCOs, which will increase the potential of compact photoelectric devices, such as optical sensing, narrowband filtering, non-radiative data transmission and biomolecular manipulation.

All-dielectric metasurface refractive index sensor with high figure of merit based on quasi-bound states in the continuum

All-Dielectric metasurfaces are widely used in the field of sense due to their small size, freedom of design, and low radiation loss. However, the optical sensor still has the problem of wide full width at half maximum (FWHM), which leads to a low figure of merit (FOM). In order to solve this problem, an all-dielectric metasurface based on quasi-bound states in the continuum (q-BIC) was proposed for refractive index sensing. The sensor structure consisted of a prism/metasurface/analyte, where the metasurface was composed of periodically arranged subwavelength asymmetric silicon gratings. The asymmetry of the structure led to the coupling of the tangential and radiative field components in the superficial layer at the resonance position, which formed a q-BIC resonance peak with a narrow FWHM in the reflection spectrum. We explained the causes of the q-BIC resonance peak generation by finite element analysis, and analyzed the factors affecting the FWHM, and also simulated the machining errors. The results showed that by reducing the asymmetry of the sensor, it could have a high FOM, with a FOM of 1.35 × 107 RIU−1. In addition, simulated machining errors within ±5 nm showed that small machining errors did not lead to the disappearance of q-BIC, which proved that the sensor had good robustness. These findings had provided ideas for the accurate detection of trace substances.

Simple A–D–A pure blue fluorescent emitters based on hybridized local and charge-transfer excited state for non-doped OLEDs with narrow full width at half-maximum of 0.20 eV and CIEy< 0.06

Narrowband emitters possess great potential in organic light emitting diodes (OLEDs) to achieve high color purity. However, developing highly efficient pure blue emitters with a simultaneously narrow full width at half-maximum (FWHM) value is a major challenge due to the energy-gap law and molecular stacking effect. Few efforts have focused on this challenging pursuit. Herein, an ingenious synthetic method was devised to achieve pure blue emitters incorporating bulky rigid planes as donors and highly twisted steric units as acceptors. Four emitters with aggregation-induced emission (AIE) characteristics, namely BCzPPM, BC-zPSP, IDCz-DBPM, and IDCz-BPSP, have been developed and used to fabricate non-doped devices. IDCz-BPSP achieves narrowed photoluminescence (PL) and electroluminescence (EL) with the benefit of suppressing vibronic coupling. Non-doped OLEDs based on IDCz-BPSP have achieved maximum external quantum efficiency (EQEmax) of 4.61% with a FWHM of 25 nm/0.20 eV. The Commission Internationale de L'Eclairage (CIE) coordinates was (0.154, 0.059), with CIEy being superior to the standard of European Broadcasting Union (EBU) 0.06. The hybridized local and charge-transfer (HLCT) states of IDCz-BPSP have simultaneously boosted the PL efficiency and exciton utilization. The EL process has even achieved exciton utilization at exceeding the theoretical limit of 25%. These results indicate that the strategy of combining bulky rigid plane donor units and steric hindrance effect is a favorable strategy for constructing emitters with narrow FWHM.

Plasmonic gold disk nanoarrays-based surface lattice resonance sensor with high figure of merit and its near-field and far-field coupling characteristics

In the field of localized surface plasmon resonance sensing, narrow linewidth, high-quality factor, and high absorptivity have always been the goals that researchers are committed to achieving. The primary methods for achieving this goal are near-field coupling and far-field coupling. Due to the limitations of nanomanufacturing processes, current research often only focuses on single coupling methods such as far-field coupling or near-field coupling, with few relevant reports combining the two coupling methods. Based on this, this paper proposes a single-layer gold nano-disk array structure, which is simple and easy to manufacture. Through modal field analysis and structural parameter adjustment, some significant results have been achieved. On the one hand, the suggested gold nano-disk array structure yields a resonant peak based on far-field coupling with a full width at half maximum (FWHM) of less than 0.05 nm and a figure of merit of more than 15 000 (the quality factor is more than 20 000). On the other hand, it has been successfully accomplished to combine near-field coupling and far-field coupling, leading to a composite coupling peak that incorporates the benefits of both types of coupling. Moreover, this coupling peak has excellent characteristics such as narrow FWHM (less than 3 nm) and high absorptivity (up to 80.5%), which is superior to most reported sensing structures and more in line with practical sensing application requirements. In this paper, the potential of the gold disk array structure as a high-performance sensing structure is further explored, providing reference and new ideas for the design of easy-to-prepare and high-performance electromagnetic resonance devices.

Ultra-Narrow-Bandwidth Deep-Red Electroluminescence Based on Green Plant-Derived Carbon Dots.

Deep-red light-emitting diodes (DR-LEDs, >660nm) with high color-purity and narrow-bandwidth emission are promising for full-color displays and solid-state lighting applications. Currently, the DR-LEDs are mainly based on conventional emitters such as organic materials and heavy-metal based quantum dots (QDs) and perovskites. However, the organic materials always suffer from the complicated synthesis, inferior color purity with full-width at half-maximum (FWHM) more than 40 nm, and the QDs and perovskites still suffer from serious problems related to toxicity. Herein, this work reports the synthesis of efficient and high color-purity deep-red carbon dots (CDs) with a record narrow FWHM of 21nm and a high quantum yield of more than 50% from readily available green plants. Moreover, an exciplex host is further established using a polymer and small molecular blend, which has been shown to be an efficient strategy for producing high color-purity monochrome emission from deep-red CDs via Förster energy transfer (FET). The deep-red CD-LEDs display high color-purity with Commission Internationale de l'Eclairage (CIE) coordinates of (0.692, 0.307). To the best of the knowledge, this is the first report of high color-purity CD-LEDs in the deep-red region, opening the door for the application of CDs in the development of high-resolution light-emitting display technologies.

In-situ neodymium ion doping into perovskite nanocrystals over ex-situ and its importance in triclosan sensing

All inorganic cesium lead halide (CsPbX3, X = Cl, Br or I) perovskite nanocrystals (NCs) exhibit wide absorption range and narrow bandwidth emission. However, the presence of defects leads to lack of long term stability and reduced photoluminescence quantum yield (PLQY). Herein, we have studied the effect of in-situ and ex-situ doping of Nd3+ into CsPbBr3 matrix to understand the importance of technique of doping and its influence on perovskite properties. It was found that optimum concentration (6%) of in-situ doping of Nd3+ into CsPbBr3 enhances PLQY by 20% and lifetime by 23 ns, whereas ex-situ Nd3+ doping shows quenching of PL. Dopant precursor was carefully chosen to avoid any anion exchange/addition unlike in previously reported studies. The exceptional quantum yields of in-situ doped Nd-CsPbBr3 NCs with narrow full width half maximum allows intense fluorescence emission and the enhanced PL helped us to utilize this as highly sensitive probe for rapid detection of a model pollutant triclosan. The enhancement in PL through in-situ doping enhances the detection levels by one order of magnitude to achieve up to nM concentration. The triclosan sensing mechanism is proved to be dynamic quenching substantiated by temperature dependent PL and lifetime decay study. This work provides insights into use of appropriate doping techniques to attain enhanced and controlled properties, through which we could reach higher detection limits in such perovskite sensing systems.

Tailoring Extremely Narrow FWHM in Hypsochromic and Bathochromic Shift of Polycyclo-Heteraborin MR-TADF Materials for High-Performance OLEDs.

Developing double boron-based emitters with extremely narrow band spectrum and high efficiency in organic light-emitting diodes (OLEDs) is crucial and challenging. Herein, we report two materials, NO-DBMR and Cz-DBMR, hinge on polycyclic heteraborin skeletons based on role-play of the highest occupied molecular orbital (HOMO) energy levels. The NO-DBMR contains an oxygen atom, whereas the Cz-DBMR has a carbazole core in the double boron-embedded ν-DABNA structure. The synthesized materials resulted in an unsymmetrical pattern for NO-DBMR and surprisingly a symmetrical pattern for Cz-DBMR. Consequently, both materials showed extremely narrow full width at half maximum (FWHM) of 14 nm in hypsochromic (pure blue) and bathochromic (Bluish green) shifted emission without losing their high color fidelity. Furthermore, both materials show high photoluminescence quantum yield (PLQY) of over 82 %, and an extremely small singlet-triplet energy gap (ΔEST ) of 0.04 eV, resulting in high reverse intersystem crossing process (kRISC ) of 105 s-1 . Due to the efficient thermally activated delayed fluorescence (TADF) characteristics, the fabricated OLEDs based on these heteraborins manifested maximum external quantum efficiency (EQEmax ) of 33.7 and 29.8 % for NO-DBMR and Cz-DBMR, respectively. This is the first work reported with this type of strategy for achieving an extremely narrow emission spectrum in hypsochromic and bathochromic shifted emissions with a similar molecular skeleton.

Tailoring Extremely Narrow FWHM in Hypsochromic and Bathochromic Shift of Polycyclo‐Heteraborin MR‐TADF Materials for High‐Performance OLEDs

AbstractDeveloping double boron‐based emitters with extremely narrow band spectrum and high efficiency in organic light‐emitting diodes (OLEDs) is crucial and challenging. Herein, we report two materials, NO‐DBMR and Cz‐DBMR, hinge on polycyclic heteraborin skeletons based on role‐play of the highest occupied molecular orbital (HOMO) energy levels. The NO‐DBMR contains an oxygen atom, whereas the Cz‐DBMR has a carbazole core in the double boron‐embedded ν‐DABNA structure. The synthesized materials resulted in an unsymmetrical pattern for NO‐DBMR and surprisingly a symmetrical pattern for Cz‐DBMR. Consequently, both materials showed extremely narrow full width at half maximum (FWHM) of 14 nm in hypsochromic (pure blue) and bathochromic (Bluish green) shifted emission without losing their high color fidelity. Furthermore, both materials show high photoluminescence quantum yield (PLQY) of over 82 %, and an extremely small singlet‐triplet energy gap (ΔEST) of 0.04 eV, resulting in high reverse intersystem crossing process (kRISC) of 105 s−1. Due to the efficient thermally activated delayed fluorescence (TADF) characteristics, the fabricated OLEDs based on these heteraborins manifested maximum external quantum efficiency (EQEmax) of 33.7 and 29.8 % for NO‐DBMR and Cz‐DBMR, respectively. This is the first work reported with this type of strategy for achieving an extremely narrow emission spectrum in hypsochromic and bathochromic shifted emissions with a similar molecular skeleton.

Triptycene-Fused Sterically Shielded Multi-Resonance TADF Emitter Enables High-Efficiency Deep Blue OLEDs with Reduced Dexter Energy Transfer.

Designing multi-resonance (MR) emitters that can simultaneously achieve narrowband emission and suppressed intermolecular interactions is challenging for realizing high color purity and stable blue organic light-emitting diodes (OLEDs). Herein, a sterically shielded yet extremely rigid emitter based on a triptycene-fused B,N core (Tp-DABNA) is proposed to address the issue. Tp-DABNA exhibits intense deep blue emissions with a narrow full width at half maximum (FWHM) and a high horizontal transition dipole ratio, superior to the well-known bulky emitter, t-DABNA. The rigid MR skeleton of Tp-DABNA suppresses structural relaxation in the excited state, with reduced contributions from the medium- and high-frequency vibrational modes to spectral broadening. The hyperfluorescence (HF) film composed of a sensitizer and Tp-DABNA shows reduced Dexter energy transfer compared to those of t-DABNA and DABNA-1. Notably, deep blue TADF-OLEDs with the Tp-DABNA emitter display higher external quantum efficiencies (EQEmax =24.8 %) and narrower FWHMs (≤26 nm) than t-DABNA-based OLEDs (EQEmax =19.8 %). The HF-OLEDs based on the Tp-DABNA emitter further demonstrate improved performance with an EQEmax of 28.7 % and mitigated efficiency roll-offs.

Triptycene‐Fused Sterically Shielded Multi‐Resonance TADF Emitter Enables High‐Efficiency Deep Blue OLEDs with Reduced Dexter Energy Transfer

AbstractDesigning multi‐resonance (MR) emitters that can simultaneously achieve narrowband emission and suppressed intermolecular interactions is challenging for realizing high color purity and stable blue organic light‐emitting diodes (OLEDs). Herein, a sterically shielded yet extremely rigid emitter based on a triptycene‐fused B,N core (Tp‐DABNA) is proposed to address the issue. Tp‐DABNA exhibits intense deep blue emissions with a narrow full width at half maximum (FWHM) and a high horizontal transition dipole ratio, superior to the well‐known bulky emitter, t‐DABNA. The rigid MR skeleton of Tp‐DABNA suppresses structural relaxation in the excited state, with reduced contributions from the medium‐ and high‐frequency vibrational modes to spectral broadening. The hyperfluorescence (HF) film composed of a sensitizer and Tp‐DABNA shows reduced Dexter energy transfer compared to those of t‐DABNA and DABNA‐1. Notably, deep blue TADF‐OLEDs with the Tp‐DABNA emitter display higher external quantum efficiencies (EQEmax=24.8 %) and narrower FWHMs (≤26 nm) than t‐DABNA‐based OLEDs (EQEmax=19.8 %). The HF‐OLEDs based on the Tp‐DABNA emitter further demonstrate improved performance with an EQEmax of 28.7 % and mitigated efficiency roll‐offs.

Multiple Helicenes Defected by Heteroatoms and Heptagons with Narrow Emissions and Superior Photoluminescence Quantum Yields**

AbstractThe incorporation of heteroatoms and/or heptagons as the defects into helicenes expands the variety of chiroptical materials with novel properties. However, it is still challenging to construct novel boron‐doped heptagon‐containing helicenes with high photoluminescence quantum yields (PLQYs) and narrow full‐width‐at‐half‐maximum (FWHM) values. We report an efficient and scalable synthesis of a quadruple helicene 4Cz‐NBN with two nitrogen‐boron‐nitrogen (NBN) units and a double helicene 4Cz‐NBN‐P1 bearing two NBN‐doped heptagons, the latter could be formed via a two‐fold Scholl reaction of the former. The helicenes 4Cz‐NBN and 4Cz‐NBN‐P1 exhibit excellent PLQYs up to 99 % and 65 % with narrow FWHM of 24 nm and 22 nm, respectively. The emission wavelengths are tunable via stepwise titration experiments of 4Cz‐NBN‐P1 toward fluoride, enabling distinguished circularly polarized luminescence (CPL) from green, orange (4Cz‐NBN‐P1‐F1) to yellow (trans/cis‐4Cz‐NBN‐P1‐F2) with near‐unity PLQYs and broader circular dichroism (CD) ranges. The five structures of the aforementioned four helicenes were confirmed by single crystal X‐ray diffraction analysis. This work provides a novel design strategy for construction of non‐benzenoid multiple helicenes exhibiting narrow emissions with superior PLQYs.