Susumu Oda

An oxygen–sulfur replacement for improving thermally activated delayed fluorescence (TADF) materials based on a multiple-resonance (MR) effect is reported. A comprehensive computational analysis of four possible isomers revealed that the precise placement of the sulfur atom is crucial to suppress undesired spectral red-shifts. Among them, a promising deep-blue emitter, DOB2-DABNA-C-NP-S-1, exhibits emission at 458 nm with a narrow full width at half maximum (FWHM) of 20 nm. Moreover, its reverse intersystem crossing rate constant (k_RISC) of 2.9 × 10⁶ s⁻¹ is three times larger than that of the oxygen-based analog (9.0 × 10⁵ s⁻¹). An OLED device incorporating DOB2-DABNA-C-NP-S-1 as an emitter achieves ultrapure deep-blue electroluminescence at 461 nm with Commission Internationale de l’Éclairage (CIE) coordinates of (0.133, 0.077), satisfying the blue emitter standards set by the National Television System Committee (NTSC). The device demonstrates outstanding external quantum efficiencies (EQEs) of 24.3% (at maximum), 23.9% (at 1000 cd m⁻²), and 18.7% (at 10 000 cd m⁻²), with the latter ranking the highest among the previously reported OLED devices employing deep-blue MR-TADF emitters.

An ultrapure deep‐blue multi‐resonance‐induced thermally activated delayed fluorescence (MR‐TADF) material (DOB2‐DABNA‐C‐NP) is synthesized as a promising emitter for organic light‐emitting diodes (OLEDs). The emission color is precisely tuned by adopting the asymmetric structure, which is modified from the previously reported symmetric compounds. Notably, the compound exhibits narrowband pure blue emission at 458 nm with a small full width at half maximum (FWHM) of 27 nm. In addition, the large π‐extended structure enables high rate constants for reverse intersystem crossing of 8.0 × 10⁵ s⁻¹. Theoretical calculations for model compounds indicate that the difference in the position of oxygen atoms significantly affects the LUMO energy levels, rationalizing the emission wavelength tuning. The OLED employing DOB2‐DABNA‐C‐NP as an emitter exhibits ultrapure deep‐blue emission at 458 nm with a small FWHM of 23 nm. This corresponds to Commission Internationale d’Éclairage (CIE) coordinates of (0.137, 0.069), which are close to the requirement for blue emitters defined by NTSC and Adobe RGB's standards. The device exhibits excellent external quantum efficiencies of 21.7% at the maximum and 20.8% at 1000 cd m⁻², demonstrating a highly suppressed efficiency roll‐off.

Efficient red-green-blue primary luminescence with an extraordinarily narrow band and durability is crucial for advanced display applications. Recently, the emergence of multiple-resonance (MR) from short-range atomic interactions has been shown to induce extremely narrow spectral widths in pure organic emitters. However, achieving wide-range color tuning without compromising color purity remains a persistent challenge for MR emitters. Herein, the concept of electronic donor/acceptor "core-shell" modulation is proposed within a boron/nitrogen (B/N) MR skeleton, enabling the rational utilization of intramolecular charge transfer to facilitate wavelength shift. The dense B atoms localized at the center of the molecule effectively compress the electron density and stabilize the lowest unoccupied molecular orbital wave function. This electron-withdrawing core is embedded with peripheral electron-donating atoms. Consequently, doping a single B atom into a deep-blue MR framework led to a profound bathochromic shift from 447 to 624 nm (∼0.8 eV) while maintaining a narrow spectral width of 0.10 eV in this pure-red emitter. Notably, organic light-emitting diodes assisted by thermally activated delayed fluorescence molecules achieved superb electroluminescent stability, with an LT₉₉ (99% of the initial luminance) exceeding 400 h at an initial luminance of 1000 cd m^-2, approaching commercial-level performance without the assistance of phosphors.

Ultrapure deep‐blue emitters are in high demand for organic light‐emitting diodes (OLEDs). Although color coordinates serve as straightforward parameters for assessing color purity, precise control over the maximum wavelength and full‐width at half‐maximum is necessary to optimize OLED performance, including luminance efficiency and luminous efficacy. Multiple‐resonance (MR) emitters are promising candidates for achieving ideal luminescence properties; consequently, a wide variety of MR frameworks have been developed. However, most of these emitters experience a wavelength displacement from the ideal color, which limits their practical applicability. Therefore, a molecular design that is compatible with MR emitters for modulating their energy levels and color output is particularly valuable. Here, it is demonstrated that the azepine donor unit induces an appropriate blue‐shift in the emission maximum while maintaining efficient MR characteristics, including high photoluminescence quantum yield, narrow emission, and a fast reverse intersystem crossing rate. OLEDs using newly developed MR emitters based on the ν‐DABNA framework simultaneously exhibit a high quantum efficiency of ≈30%, luminous efficacy of ≈20 lm W⁻¹, exceptional color purity with Commission Internationale de l’Éclairage coordinates as low as (0.14, 0.06), and notably high operational stability. These results demonstrate unprecedentedly high levels compared with those observed in previously reported deep‐blue emitters.

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.

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.

A low lasing threshold of up to 0.27 μJ cm⁻¹ was achieved by using TADF materials. Advanced light amplification architectures composed of dual DABNA derivatives were also demonstrated.

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.