Luminescent materials that exhibit narrowband emission are vital for full-colour displays. Here, we report a thermally activated delayed-fluorescence material that exhibits ultrapure blue emission ...with full-width at half-maximum of just 14 nm. The emitter consists of five benzene rings connected by two boron and four nitrogen atoms and two diphenylamino substituents. The multiple resonance effect of the boron and nitrogen atoms induces significant localization of the highest occupied and lowest unoccupied molecular orbitals on different atoms to minimize not only the vibronic coupling between the ground state (S0) and the singlet excited state (S1) but also the energy gap between the S1 state and triplet excited state (T1). Organic light-emitting diode devices employing the emitter emit light at 469 nm with full-width at half-maximum of 18 nm with an external quantum efficiency of 34.4% at the maximum and 26.0% at 1,000 cd m−2.
Thermally activated delayed fluorescence (TADF) materials based on the multiple resonance (MR) effect are applied in organic light‐emitting diodes (OLEDs), combining high color purity and efficiency. ...However, they are not fabricated via solution‐processing, which is an economical approach toward the mass production of OLED displays. Here, a solution‐processable MR‐TADF material (OAB‐ABP‐1), with an extended π‐skeleton and bulky substituents, is designed. OAB‐ABP‐1 is synthesized from commercially available starting materials via a four‐step process involving one‐shot double borylation. OAB‐ABP‐1 presents attractive photophysical properties, a narrow emission band, a high photoluminescence quantum yield, a small energy gap between S1 and T1, and low activation energy for reverse intersystem crossing. These properties are attributed to the alternating localization of the highest occupied and lowest unoccupied molecular orbitals induced by the boron, nitrogen, and oxygen atoms. Furthermore, to facilitate charge recombination, two novel semiconducting polymers with similar ionization potentials to that of OAB‐ABP‐1 are synthesized for use as interlayer and emissive layer materials. A solution‐processed OLED device is fabricated using OAB‐ABP‐1 and the aforementioned polymers; it exhibits pure green electroluminescence with a small full‐width at half‐maximum and a high external quantum efficiency with minimum efficiency roll‐off.
A thermally activated delayed fluorescence material featuring a multiple resonance effect of boron, nitrogen, and oxygen atoms (OAB‐ABP‐1) is synthesized by one‐shot double borylation. A solution‐processed organic light‐emitting diode (OLED) device using OAB‐ABP‐1 exhibits pure green electroluminescence with a small full‐width at half‐maximum, and a high external quantum efficiency with minimum efficiency roll‐off.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Multiple resonance (MR)‐effect‐induced thermally activated delayed fluorescence (TADF) materials have garnered significant attention because they can achieve both high color purity and high external ...quantum efficiency (EQE). However, the reported green‐emitting MR‐TADF materials exhibit broader emission compared to those of blue‐emitting ones and suffer from severe efficiency roll‐off due to insufficient rate constants of reverse intersystem crossing process (kRISC). Herein, a pure green MR‐TADF material (ν‐DABNA‐CN‐Me) with high kRISC of 105 s−1 is reported. The key to success is introduction of cyano groups into a blue‐emitting MR‐TADF material (ν‐DABNA), which causes remarkable bathochromic shift without a loss of color purity. The organic light‐emitting diode employing it as an emitter exhibits green emission at 504 nm with a small full‐width at half‐maximum of 23 nm, corresponding to Commission Internationale d'Éclairage coordinates of (0.13, 0.65). The device achieves a high maximum EQE of 31.9% and successfully suppresses the efficiency roll‐off at a high luminance.
The bathochromic shift of a multiple‐resonance‐induced thermally activated delayed fluorescence material (ν‐DABNA) is achieved by introducing cyano groups. The cyano‐substituted material (ν‐DABNA‐CN‐Me) exhibits pure green emission with a small full‐width at half‐maximum. The fabricated organic light‐emitting diode device exhibits a high maximum external quantum efficiency (31.9%), which is maintained (28.5%) at 1000 cd m−2, demonstrating a minimum efficiency roll‐off.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
An expanded heterohelicene consisting of three BN2-embedded 4helicene subunits (V-DABNA-Mes) has been synthesized by one-shot triple borylation. The key to success is the excessive use of boron ...tribromide in an autoclave. Based on the multiple resonance effect of three boron and six nitrogen atoms, V-DABNA-Mes exhibited a narrowband sky-blue thermally activated delayed fluorescence with a full width at half-maximum of 16 nm. The resonating π-extension minimized the singlet–triplet energy gap and enabled rapid reverse intersystem crossing with a rate constant of 4.4 × 105 s–1. The solution-processed organic light-emitting diode device, employed as an emitter, exhibited a narrowband emission at 480 nm with a high external quantum efficiency of 22.9%.
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IJS, KILJ, NUK, PNG, UL, UM
Herein, we reported an ultrapure blue multiple‐resonance‐induced thermally activated delayed fluorescence (MR‐TADF) material (ν‐DABNA‐O‐Me) with a high photoluminescence quantum yield and a large ...rate constant for reverse intersystem crossing. Because of restricted π‐conjugation of the HOMO rather than the LUMO induced by oxygen atom incorporation, ν‐DABNA‐O‐Me shows a hypsochromic shift compared to the parent MR‐TADF material (ν‐DABNA). An organic light‐emitting diode based on this material exhibits an emission at 465 nm, with a small full‐width at half‐maximum of 23 nm and Commission Internationale de l'Eclairage coordinates of (0.13, 0.10), and a high maximum external quantum efficiency of 29.5 %. Moreover, ν‐DABNA‐O‐Me facilitates a drastically improved efficiency roll‐off and a device lifetime compared to ν‐DABNA, which demonstrates significant potential of the oxygen atom incorporation strategy.
A multiple‐resonance‐induced thermally activated delayed fluorescence material that comprised oxygen, nitrogen, and boron atoms (ν‐DABNA‐O‐Me) was synthesized via one‐shot double borylation. An OLED device employing the fabricated ν‐DABNA‐O‐Me exhibits deep‐blue electroluminescence with a small full‐width at half‐maximum and a high external quantum efficiency with minimum efficiency roll‐off.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Multiple-resonance thermally activated delayed fluorescence (MR-TADF) emitters have emerged as an important component of organic light-emitting diodes (OLEDs) because of their narrowband emission and ...high exciton utilization efficiency. However, the chemical space of MR-TADF emitters remains mostly unexplored because of the lack of suitable synthetic protocols. Herein, we demonstrate a sequential multiple borylation reaction that provides new synthetically accessible chemical space. ω-DABNA, the proof-of-concept material, exhibited narrowband green TADF with a full width at half-maximum of 22 nm and a small singlet–triplet energy gap of 13 meV. The OLED employing it as an emitter exhibited electroluminescence at 512 nm, with Commission International de l’Éclairage coordinates of (0.13, 0.73) and a high external quantum efficiency (EQE) of 31.1%. Moreover, the device showed minimum efficiency roll-off, with an EQE of 29.4% at 1000 cd m–2.
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Double 5helicenes possessing two tetracoordinated boron atoms at the ring junctions were synthesized from glycine anhydride in three steps. The helicene with fluorine substituents on the boron atoms ...was employed as a cathode active material in a lithium battery to demonstrate moderate performance in the 1.8–3.5 V range with more than 63 mAh g–1 discharge capacity for 20 cycles and high Coulombic efficiency of over 90%.
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BN-embedded nonacene, tridecacene, and heptadecacene frameworks were constructed using one-shot quadruple, sextuple, and octuple borylation reactions, respectively. The key to success is the ...judicious choice of borylating reagents and long-chain alkyl-substituted carbazolyl groups as boron-trapping groups, which suppressed the decrease in HOMO energy and insolubilization associated with borylation. Based on the product yields, each electrophilic C–H borylation proceeded in >99% yield, which is the best efficiency reported so far for C–H borylation reactions. Owing to the multiple resonance effects of boron and nitrogen, the prepared acenes exhibited ultra-narrowband green thermally activated delayed fluorescence with full-width at half-maximum of 12–16 nm; moreover, their k RISC values were in the order of 105 s–1. We fabricated an organic light-emitting diode by employing the nonacene as an emitter, which exhibited high external quantum efficiency (EQE) of 28.7%. The device also showed a minimum efficiency roll-off with an EQE of 25.8% at 1000 cd m–2.
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