Masakazu Kondo

Multiple‐resonance thermally activated delayed fluorescence (MR‐TADF) emitters are promising candidates for organic light‐emitting diodes owing to their narrowband emission and high exciton utilization. While π‐conjugated framework expansion has been extensively explored for tuning excited‐state properties, five‐boron MR‐TADF emitters have not yet been realized. Herein, we report the first five‐boron MR‐TADF emitter, M‐DABNA‐Mes, featuring an unprecedented odd‐numbered boron‐rich multiple‐resonance framework. Theoretical investigations of one‐, three‐, and five‐boron MR frameworks reveal that incorporation of the fifth boron atom reduces the singlet–triplet energy gap, preserves spin–orbit coupling, and reduces the total reorganization energy while maintaining favorable narrowband emission characteristics. Consistent with these predictions, M‐DABNA‐Mes doped in a polystyrene film exhibits a sub‐microsecond delayed fluorescence lifetime ( τ _TADF = 0.93 µs), a reverse intersystem crossing rate of 2.6 × 10 ⁶ s ⁻¹ , and narrow green emission at 512 nm with a full width at half maximum of 19 nm. OLEDs based on M‐DABNA‐Mes achieve a maximum external quantum efficiency of 34.3% with remarkably low efficiency roll‐off (32.3% at 10,000 cd m ⁻² ) and a maximum luminance of 275,800 cd m ⁻² . These results demonstrate that the five‐boron MR framework enables rapid spin conversion, high spectral purity, and excellent OLED performance, providing a new platform for high‐performance MR‐TADF emitters.

Multiple‐resonance thermally activated delayed fluorescence (MR‐TADF) emitters are promising candidates for organic light‐emitting diodes owing to their narrowband emission and high exciton utilization. While π‐conjugated framework expansion has been extensively explored for tuning excited‐state properties, five‐boron MR‐TADF emitters have not yet been realized. Herein, we report the first five‐boron MR‐TADF emitter, M‐DABNA‐Mes, featuring an unprecedented odd‐numbered boron‐rich multiple‐resonance framework. Theoretical investigations of one‐, three‐, and five‐boron MR frameworks reveal that incorporation of the fifth boron atom reduces the singlet–triplet energy gap, preserves spin–orbit coupling, and reduces the total reorganization energy while maintaining favorable narrowband emission characteristics. Consistent with these predictions, M‐DABNA‐Mes doped in a polystyrene film exhibits a sub‐microsecond delayed fluorescence lifetime ( τ _TADF = 0.93 µs), a reverse intersystem crossing rate of 2.6 × 10 ⁶ s ⁻¹ , and narrow green emission at 512 nm with a full width at half maximum of 19 nm. OLEDs based on M‐DABNA‐Mes achieve a maximum external quantum efficiency of 34.3% with remarkably low efficiency roll‐off (32.3% at 10,000 cd m ⁻² ) and a maximum luminance of 275,800 cd m ⁻² . These results demonstrate that the five‐boron MR framework enables rapid spin conversion, high spectral purity, and excellent OLED performance, providing a new platform for high‐performance MR‐TADF emitters.

Thermally activated delayed fluorescence (TADF) materials are promising emitters for organic light‐emitting diodes (OLEDs) owing to their ability to harvest both singlet and triplet excitons. However, realizing pure‐green, narrowband emission with simultaneously high efficiency and stability remains a long‐standing challenge for display applications. In this study, we report a concise one‐shot double borylation strategy uniquely enabled by chlorine substituents acting as both directing and functional groups. This dual role not only ensures regioselective synthesis of a π‐extended multiple resonance (MR) framework—previously considered synthetically inaccessible—but also provides versatile handles for late‐stage diversification. The resulting key intermediate, W‐DABNA‐Cl , was obtained in 48% yield and readily converted into a series of structurally diverse MR‐TADF emitters through single‐step derivatizations. These emitters exhibited narrowband emissions from deep green to yellow‐green (FWHM 27–34 nm) with tunable photophysical properties. Notably, TADF‐sensitized fluorescence devices based on W‐DABNA‐Cz achieved an excellent maximum external quantum efficiency (EQE) of 36.1%. More importantly, the device maintained record‐high efficiencies of 34.3% and 29.5% at luminance levels of 1000 and 10 000 cd m ⁻² , respectively, representing the best efficiency–brightness trade‐off among reported green sensitized OLEDs. This work not only overcomes synthetic bottlenecks in accessing π‐extended MR‐TADF frameworks but also establishes a versatile platform for color‐tunable, high‐performance OLEDs.

Thermally activated delayed fluorescence (TADF) materials are promising emitters for organic light‐emitting diodes (OLEDs) owing to their ability to harvest both singlet and triplet excitons. However, realizing pure‐green, narrowband emission with simultaneously high efficiency and stability remains a long‐standing challenge for display applications. In this study, we report a concise one‐shot double borylation strategy uniquely enabled by chlorine substituents acting as both directing and functional groups. This dual role not only ensures regioselective synthesis of a π‐extended multiple resonance (MR) framework—previously considered synthetically inaccessible—but also provides versatile handles for late‐stage diversification. The resulting key intermediate, W‐DABNA‐Cl , was obtained in 48% yield and readily converted into a series of structurally diverse MR‐TADF emitters through single‐step derivatizations. These emitters exhibited narrowband emissions from deep green to yellow‐green (FWHM 27–34 nm) with tunable photophysical properties. Notably, TADF‐sensitized fluorescence devices based on W‐DABNA‐Cz achieved an excellent maximum external quantum efficiency (EQE) of 36.1%. More importantly, the device maintained record‐high efficiencies of 34.3% and 29.5% at luminance levels of 1000 and 10 000 cd m ⁻² , respectively, representing the best efficiency–brightness trade‐off among reported green sensitized OLEDs. This work not only overcomes synthetic bottlenecks in accessing π‐extended MR‐TADF frameworks but also establishes a versatile platform for color‐tunable, high‐performance OLEDs.

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.

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.

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.

A new generative model, in which the Variational Autoencoder network is combined with the Transformer architecture, is developed. The proposed model, the Variational Autoencoding Transformer (VAT), is applied to the task of generating molecules, showing that, with proper training, the VAT model can not only produce similar molecules to input ones with high accuracy but also generate new molecules from a predefined prior almost perfectly. A desirable aspect of our VAT is that no heuristic setting is necessary for optimal performance, which suggests that the model can readily be available to a variety of datasets. As practical directions toward materials/drug discovery, two strategies: a fine‐tuning method for directed molecular generation and a method of mixing molecules in the latent space, are demonstrated.