Rong-Huei Yi

Integrating chiral elements within a multi-resonance framework presents a promising avenue for engineering tailored emitters suited to cutting-edge circularly polarized organic light–emitting diodes. Consequently, a considerable g _PL of 3.3 × 10⁻³ along with exceptional device performance characterized by a peak external quantum efficiency of 36.6%, and desirable CIE coordinates (0.19, 0.71) can be achieved simultaneously.

Abstract

The integration of chiral elements within a multiple resonance (MR) motif affords a prospective avenue to construct satisfying emitters tailored for state-of-the-art circularly polarized organic light–emitting diodes (CP-OLEDs). However, the concurrently realizing of both high luminescence efficiency and favorable dissymmetry factors (g _PL) still remains a formidable challenge, particularly when aligning with the requirement of high color purity. Herein, a dual-pronged approach is proposed to reconcile such trade-offs by directly fusing a secondary chiral donor onto the MR scaffold, thereby facilitating a hybrid short/long-range charge-transfer with fine-tuned compositions. Theoretical calculations unveil the pronounced impact of the chiral donor on meticulously refining the characteristics of excited states, therefore yielding a considerable g _PL of 3.3 × 10⁻³, along with a high fluorescence quantum yield of 0.97, and a rapid reverse intersystem crossing rate of 3.06 × 10⁵ s⁻¹ in one embodiment. Leveraging these merits, electroluminescence devices incorporating them as chiral dopants exhibit exceptional performance, showcasing a peak external quantum efficiency of 36.6% and remarkable Commission Internationale de L'Eclairage coordinates of (0.19, 0.71), which represent one of the most notable achievements among pure-green CP-OLEDs.

A strategy of controlling electron density on amino of diaminoterephthalates to modulate their photophysical properties and functionalities is proposed. Based on this strategy, a series of single-benzene fluorophores is facilely synthesized and exhibits tunable bright dual-state emission in solution and solid-state, acidichromism, Cu²⁺ detection, and lipid droplets staining.

Abstract

Single-benzene fluorophores have attracted increasing interest owing to their simple molecular structure and unique photophysical properties. Developing novel single-benzene fluorophores with facile synthesis, bright and tunable dual-state emissions, and diversified functions is highly desirable. Herein, a strategy of controlling electron density on amino of 2,5-diaminoterephthalates is proposed to modulate their dual-state emission, acidichromism, Cu²⁺ detection, and lipid droplets (LDs) staining. A series of efficient dual-state single-benzene fluorophores based on 2,5-diaminoterephthalate skeleton with tunable emissions in blue to red region and large Stokes shifts is facilely developed. The obtained fluorophores with various substituents on amino groups exhibit different acidichromism property. Two of fluorophores (ABB and ABM) with high electron density on amino groups exhibit high sensitivity and selectivity toward Cu²⁺ detection with a ratiometric and “turn-off” fluorescence mechanism for ABM and ABB, respectively. The limit of detection for Cu²⁺ is determined to be 1.40 × 10⁻⁷ and 4.35 × 10⁻⁹ mol L⁻¹ for ABB and ABM, respectively. Moreover, three of fluorophores (ABT, ABB, and ABM) with green to red emission display superior LDs-targeting capability with high specificity, and brightness. This molecular design philosophy provides a new way of designing highly bright dual-state fluorophores for practical applications.

Abstract

Linear gold complexes of the “carbene-metal-amide” (CMA) type are prepared with a rigid benzoguanidine amide donor and various carbene ligands. These complexes emit in the deep-blue range at 424 and 466 nm with 100% quantum yields in all media. The deep-blue thermally activated delayed fluorescence (TADF) originates from a charge transfer state (CT) with an excited state lifetime as low as 213 ns, resulting in fast radiative rates of 4.7 × 10⁶ s⁻¹. The high thermal and photo-stability of these CMA materials enabled us to fabricate highly energy efficient organic light-emitting diodes (OLED) in host-guest architectures. We report deep-blue OLED devices with electroluminescence at 416 nm and 457 nm with practical external quantum efficiencies of up to 23% at 100 cd m⁻² with excellent colour coordinates CIE (x; y) = 0.16; 0.07 and 0.17; 0.18. The operating stability of these OLEDs is the longest reported to date (LT₅₀ = 1 hour) for deep-blue CMA emitters, indicating a high promise for further development of blue OLED devices. Our findings inform the molecular design strategy and correlation between delayed luminescence with high radiative rates and CMA OLED device operating stability.

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An organic solid-state laser under continuous-wave (CW) excitation is one of the most challenging areas in organic optoelectronics. Recent advances in long-pulsed organic lasers are comprehensively summarized with respect to molecular designs, optical-resonator architectures, triplet scavenging, and potential triplet-contribution strategies. Future directions and perspectives for CW operation are discussed.

Abstract

A continuous-wave (CW) organic solid-state laser is highly desirable for spectroscopy, sensing, and communications, but is a significant challenge in optoelectronics. The accumulation of long-lived triplet excitons and relevant excited-state absorptions, as well as singlet–triplet annihilation, are the main obstacles to CW lasing. Here, progress in singlet- and triplet-state utilizations in organic gain media is reviewed to reveal the issues in working with triplets. Then, exciton behaviors that inhibit light oscillations during long excitation pulses are discussed. Further, recent advances in increasing organic lasing pulse widths from microseconds toward the indication of CW operation are summarized with respect to molecular designs, advanced resonator architectures, triplet scavenging, and potential triplet contribution strategies. Finally, future directions and perspectives are proposed for achieving stable CW organic lasers with significant triplet contribution.

A promising light-pressing modulated nanowelding process is proposed for fabricating large-area AgNWs flexible transparent conductive electrodes (FTCEs) toward next generation flexible optoelectronics, and the resulting AgNWs FTCEs-based green phosphorescent organic light-emitting diode achieves an unprecedented external quantum efficiency of 23.7% and a current efficiency as high as 81.5 cd A⁻¹, demonstrating a uniform large-area emission of 25 × 25 mm².

Abstract

Despite considerable interest, uniform and robust flexible transparent conducting electrodes (FTCEs) that can be seamlessly integrated and used for highly efficient large-area flexible oganic light-emitting diodes (OLEDs) remain elusive. In this study, a large-area fabrication of uniform transparent electrodes for high-performance flexible OLEDs by exploiting the rapid nanowelding process of silver nanowires (AgNWs) onto polyethylene terephthalate substrate under Xe-lamp irradiation and mechanical pressing treatment is reported. The performance of AgNWs FTCEs is significantly enhanced by applying the Xe-lamp beam irradiation for 5 s and subsequent compression at 20 MPa for 15 s, achieving a low sheet resistance of 26.5 Ω sq⁻¹, a high transmittance of 95.2% (at 550 nm), and very smooth surfaces with root-mean-square of 5.4 nm. Meanwhile, the nanowelded AgNWs FTCEs maintain excellent electrical conductivity (only a 2.96% increase in ΔR/R ₀) after 1000 bending cycles. The resulting AgNWs FTCEs-based green phosphorescent OLED achieves an unprecedented external quantum efficiency (EQE) of 23.7% and a current efficiency as high as 81.5 cd A⁻¹. Benefiting from the uniform properties for resulting AgNWs FTCEs, the fabricated flexible OLED with a large area of 25 × 25 mm² still retains a high EQE of 22.2% and a current efficiency of 78.0 cd A⁻¹ _.

Currently, much research effort has been devoted to improving the exciton utilization efficiency and narrowing the emission spectra of ultraviolet (UV) fluorophores for organic light-emitting diode (OLED) applications, while almost no attention has been paid to optimizing their light out-coupling efficiency. Here, we developed a linear donor-acceptor-donor (D-A-D) triad, namely CDFDB, which possesses high-lying reverse intersystem crossing (hRISC) property. Thanks to its integrated narrowband UV photoluminescence (PL) (λPL: 397 nm; FWHM: 48 nm), moderate PL quantum yield (φPL: 72%, Tol), good triplet hot exciton (HE) conversion capability, and large horizontal dipole ratio (Θ//: 92%), the OLEDs based on CDFDB not only can emit UV electroluminescence with relatively good color purity (λEL: 398 nm; CIEx,y: 0.161, 0.040), but also show a record maximum external quantum efficiency (EQEmax) of 12.0%. This study highlights the important role of horizontal dipole orientation engineering in the molecular design of HE UV-OLED fluorophores.

A ternary charge-transfer (CT) cocrystal with weakened exciton coupling strength due to the changed geometric structure and enlarged donor-acceptor distance is successfully synthesized by rationally selecting monomers. This leads to a prolonged CT exciton lifetime which remarkably improves its photocurrent response and photocatalytic performance, highlighting the future application of CT cocrystals in light conversion.

Abstract

Charge-transfer (CT) cocrystals have attracted continuous interest for their promising optical and optoelectronic applications. To improve the performance of this class of material, a CT cocrystal with long-lived CT excitons is highly desired. Herein, the development of a pyrene-doped trans-1,2-diphenylethylene-1,2,4,5-tetracyanobenzene ternary cocrystal (named P-T_S-T_C) is reported. Compared to the undoped binary cocrystals (without pyrene), P-T_S-T_C exhibits a two times longer CT exciton lifetime (≈60.2 ns), and thus 8.8- and 16.6-times improvement in photocurrent response and photocatalytic H₂ evolution activity. By using transient photoluminescence spectroscopy, it is uncovered that the absorbed photon energy in P-T_S-T_C is localized to a lower energy CT state through an efficient energy transfer process (≈389.8 ps) between two co-existing CT states. The CT exciton lifetime is prolonged due to the weakened CT coupling strength, as a result of the enlarged donor-acceptor distance and the change of geometric structure. The result is expected to inspire the design of cocrystals with manipulatable CT exciton properties and to promote the potential application of multi-component CT cocrystals.

Nature, Published online: 08 May 2024; doi:10.1038/s41586-024-07246-x

Nature, Published online: 08 May 2024; doi:10.1038/d41586-024-01170-w

Abstract

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, we demonstrate 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.

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Two TADF emitters, APTT and APTI, which have the same D/A backbone but different attaching groups at the APDC core, are reported. The appended regulating groups can not only suppress the D/A rotation due to the space confinement effects but also modulate the locally excited triplet state (³LE). This work can provide an effective approach for researchers to develop red/NIR TADF emitters.

Abstract

Developing highly efficient red/near-infrared (NIR) thermally activated delayed fluorescence (TADF) materials is important for organic light-emitting diodes (OLEDs). Here, two TADF emitters, APTT and APTI, which have the same D/A backbone but different attaching groups at acenaphtho-[1,2-b]pyrazine-8,9-dicarbonitrile (APDC) core, are reported. The appended regulating groups can not only suppress the D/A rotation due to the space confinement effects but also modulate the locally excited triplet state (³LE). The improved molecular rigidity suppresses the non-radiative process, accounting for the improved photoluminescence quantum yields (PLQYs), while the modulated ³LE promotes the reverse intersystem crossing (RISC) process due to the high utilization efficiency of triplets. Consequently, both APTT and APTI demonstrate high PLQY and fast RISC process, thereby enhancing TADF efficiency. The doped devices based on APTT and APTI achieve maximum external quantum efficiency (EQE_max) values of 20.5% and 25.4% with emission peaks at 664 and 670 nm, respectively. The non-doped devices of APTT and APTI achieve the EQE_max of 2.8% and 2.9% with emission peaks at 788 and 794 nm, respectively. Encouragingly, the non-doped devices of APTI have set new records for near-infrared TADF OLEDs based on the APDC core. This study provides an efficient approach to modulating the optoelectronic properties of highly efficient NIR TADF OLEDs.

The strategy of peripheral Se modification is proposed to disclose the impact of heavy atom on the structure-performance relationship of blue MR-TADF emitters. As the proof of concept, the OLEDs based on Se-modified emitters achieved excellent performances, with a maximum EQE of 25.5% and the EQE still maintains to be 24.5% and 19.6% at the luminance of 100 and 1000 cd m^-2, respectively.

Abstract

Multi-resonance thermally activated delayed fluorescence (MR-TADF) molecules have attracted much attention in the academia owing to their unique photoelectrical properties. However, MR-TADF emitters usually show slow reverse intersystem crossing (RISC) rate, resulting in high efficiency roll-off of organic light-emitting diodes (OLEDs) and seriously limiting their further development. Here, a peripheral selenium (Se) modification is presented for MR-TADF molecules to promote the RISC process while keeping the narrowband emission for high-performance blue OLEDs. Compared to the parent molecules (NBN and tBuNBN), SeNBN and SetBuNBN exhibited narrower full-width at half maximum (FWHM) value of 23 nm and more obvious delayed fluorescence properties with a high efficiency of delayed fluorescence up to 86%, shorter delayed lifetime of 2.4 µs as well as a faster RISC rate of 3.34×10⁵ s⁻¹. Therefore, high-performance OLEDs based on these two Se modified MR-TADF emitters are achieved with a high maximum external quantum efficiency (EQE) up to 25.5% and extremely suppressed efficiency roll-offs of 3.9% at 100 cd m⁻² and 24.4% at 1000 cd m⁻². This work demonstrated that the introduction of peripheral Se atom can achieve high-performance organic semiconductors with both narrowband emission and fast RISC rate constant for high-performance organic optoelectronic devices.

The significant impact of the deuteration of both host and guest molecules on NIR photoluminescence properties in the codeposited film is observed. The codeposited film exhibits PLQY of ≈15% with an emission peak wavelength at 900 nm, which is about three times higher than the film composed of un-deuterated molecules.

Abstract

Near-infrared organic light-emitting diodes (NIR-OLEDs) possess substantial potential for future valuable applications, such as a light source for sensing applications. However, the low photoluminescence quantum yield (PLQY) of NIR-emitting molecules represents a significant impediment to these applications. In this study, the impact of the deuteration of both of host (mCP-d₂₀ : 1,3-Dicarbazole-benzene-d₂₀ ) and guest (BBT-TPA-d₂₈ : 4,8-bis[4-(N,N-diphenylamino)phenyl]benzo[1,2-c:4,5-c']bis[1,2,5]thiadiazole-d₂₈ ) on NIR PL properties in the host–guest codeposited film is reported. The 1 wt%-BBT-TPA-d₂₈ :mCP-d₂₀ codeposited film exhibited PLQY of 15 ± 2% with an emission peak wavelength at ≈900 nm, which is about three times higher than that of the film composed of undeuterated molecules. Importantly, the deuteration of only the host or guest does not yield the PLQY up to 15%, underlining the importance of the deuteration of both host and guest molecules in suppressing nonradiative decay processes. The NIR-OLED with the deuterated codeposited film as an emissive layer demonstrates a maximum external electroluminescence quantum efficiency of 2.3 ± 0.2%.

The application of intramolecular non-covalent π–π interactions is broadened to the realm of single-molecule optoelectronic emitters, by featuring a face-to-face donor/acceptor stacking configuration with efficient through-space charge transfer. The resulting supramolecular foldamer showcases that the high-performance single-molecule exciplex thermally activates delayed fluorescence and demonstrates a record lifetime of 236 milliseconds for single-molecule deep-blue room temperature phosphorescence with a charge transfer feature.

Abstract

Although the π–π stacking has been widely applied for constructing aggregated emitters in optoelectronics fields, the role of intramolecular non-covalent π–π interactions has not been well studied. Here, a supramolecular foldermer M-σ-C, with the electron donor (D) and acceptor (A) units spatially separated with a non-covalent bond at a close distance by methylene linker is designed and synthesized. This gives a face-to-face D/A stacking configuration with supramolecular π–π interactions. Temperature-dependent nuclear magnetic resonance measurements and single crystal analyses confirm its folding configuration. In solutions, M-σ-C exhibits a single-molecule exciplex thermally activated delayed fluorescence (TADF) property ascribing to the efficient intramolecular through-space charge transfer (CT) process. While single-molecule deep-blue room temperature phosphorescence (RTP) with a long afterglow lifetime of 236 ms is observed in a nonpolar matrix, which represents the record lifetime among current ³CT-character featured RTP. This work indicates that intramolecular non-covalent interactions play an important role in manipulating high-performance single-molecule exciplex TADF and RTP, and provide a feasible molecular design strategy for supramolecular chemistry involving the development of optoelectronic materials.

A novel acceptor–donor–acceptor type molecular skeleton is designed to realize blue thermally activated delayed fluorescence with ultrahigh emission efficiencies (up to 99%), nanosecond exciton lifetimes, and effectively suppressed concentration quenching in films. The doped and nondoped organic light-emitting diodes attain high external quantum efficiencies up to 32.0% and 26.6%, respectively.

Abstract

Simultaneously achieving a high photoluminescence quantum yield (PLQY), ultrashort exciton lifetime, and suppressed concentration quenching in thermally activated delayed fluorescence (TADF) materials is desirable yet challenging. Here, a novel acceptor–donor–acceptor type TADF emitter, namely, 2BO-sQA, wherein two oxygen-bridged triarylboron (BO) acceptors are arranged with cofacial alignment and positioned nearly orthogonal to the rigid dispirofluorene-quinolinoacridine (sQA) donor is reported. This molecular design enables the compound to achieve highly efficient (PLQYs up to 99%) and short-lived (nanosecond-scale) blue TADF with effectively suppressed concentration quenching in films. Consequently, the doped organic light-emitting diodes (OLEDs) base on 2BO-sQA achieve exceptional electroluminescence performance across a broad range of doping concentrations, maintaining maximum external quantum efficiencies (EQEs) at over 30% for doping concentrations ranging from 10 to 70 wt%. Remarkably, the nondoped blue OLED achieves a record-high maximum EQE of 26.6% with a small efficiency roll-off of 14.0% at 1000 candelas per square meter. By using 2BO-sQA as the sensitizer for the multiresonance TADF emitter ν-DABNA, TADF-sensitized fluorescence OLEDs achieve high-efficiency deep-blue emission. These results demonstrate the feasibility of this molecular design in developing TADF emitters with high efficiency, ultrashort exciton lifetime, and minimal concentration quenching.

By strategic manipulating the positions of the heavy atom selenium in multiple resonance thermally activated delayed fluorescence emitters, the role of heavy atom selenium in enhancing heavy atom effect and spin-orbital coupling are elucidated. Efficient triplet harvesting and well-suppressed efficiency roll-off are achieved by adopting the developed emitter with 3-substituted phenoxaselenine.

Abstract

In the development of organic light-emitting diodes (OLEDs) with high efficiency and minimal efficiency roll-off, fast reverse intersystem crossing (RISC) in multi-resonance thermally activated delayed fluorescence (MR-TADF) materials is critical. The RISC process is typically hindered by insufficient spin-orbital coupling (SOC). Incorporating heavy atom selenium into the MR-TADF structure has the potential to enhance SOC through the heavy atom effect. However, the specific placement of selenium within the molecule results in different enhancements of SOC, with the detailed interplay between these factors yet to be elucidated. The introduction of a selenium-containing moiety, phenoxaselenine, into the MR-TADF structure at different substituted positions is undertaken, revealing that the molecule with 3-substituted phenoxaselenine exhibits faster RISC transition and a significant increase in SOC between higher triplet excited states and S₁ state, compared to the molecule with 2-substituted phenoxaselenine. Significantly reduced efficiency roll-off is achieved for the narrow-band emission OLEDs based on the molecule with 3-substituted phenoxaselenine owing to the enhanced heavy atom effect, giving an impressive external quantum efficiency above 20% even under 10 000 cd m⁻² in the corresponding OLED device. These results underscore the potential of strategic heavy atom effect manipulation in MR-TADF materials for efficient spin-flipping.

The Table of Contents (TOC) image illustrates that novel organic supramolcular macrocycle scintillators with guest-induced TADF emission via host-guest through-space charge transfers, enabling efficient and color-tunable X-ray luminescence, as well as high-resolution imaging of 20 lp mm⁻¹ in devices.

Abstract

Organic scintillators, pivotal in security and medical applications, face challenges due to limited X-ray absorption and exciton utilization. Herein, a novel class of organic scintillators is introduced, named guest-induced thermally activated delayed fluorescence (TADF) within supramolecular macrocycles via host-guest through-space charge transfer (TSCT). Four co-crystals are obtained through orthogonal crystallizations involving calix[3]acridan (C[3]A) and calix[3]phenothiazine (C[3]P) macrocycles as hosts, along with 1,2-dicyanobenzene (DCB) and 4-bromo-1,2-benzenedicarbonitrile (BrDCB) as guests. Interestingly, DCB@C[3]A and BrDCB@C[3]A co-crystals exhibit strong host-guest TSCT with reduced single-triplet energy gap for efficient TADF emission, which leads to enhanced exciton utilization and X-ray absorption, yielding radioluminescence intensities over 29 and 25 times higher than C[3]A. Similarly, substituting C[3]A with C[3]P, the obtained TADF co-crystals also outperform C[3]P in scintillation performance. Additionally, the scintillation color of co-crystals can be adjusted by varying the electron-donating abilities of macrocycles and the electron-accepting abilities of guests, offering a simpler color-tuning mechanism than covalent-bonded scintillators. Furthermore, the flexible film based on DCB@C[3]A exhibits promising application in X-ray radiography, showcasing a high spatial resolution of 20 lp mm⁻¹ @MTF = 0.77. The innovative strategy of fabricating organic scintillators via reversible non-covalent interactions presents a novel solution for designing color-tunable and high-performance scintillators.

This study provides a better understanding of the degradation mechanism of blue organic light-emitting diodes (OLEDs) related to the molecular structures of electron transport materials (ETMs). The photodegradation experiment combined with electric currents indicates the importance of stability against hole currents for triazine-based ETMs. The optimized device shows better durability compared to the reference hyperfluorescence OLED.

Abstract

Recent advances in organic light-emitting diodes (OLEDs) based on thermally activated delayed fluorescence (TADF)-assisted fluorescence (TAF) attest to the great promise of this technology in practical use. However, the simultaneous realization of high efficiency and device durability in blue OLEDs remains a significant challenge. Clarification of the degradation mechanisms correlated to molecular structure and device configuration is the key to extending the device lifetime. In this study, electron transport materials incorporating two triazine units in close proximity are adopted to use in hole-blocking and electron-transporting layers, resulting in superior device performances. In addition, a modified photodegradation experiment reveals that the degradation origins closely relate to charge carriers. The optimization of the device according to the obtained findings leads to 4.5 times extension in the lifetime of the TAF-OLED using a multiple resonance emitter. These results also provide guidelines for designing robust electron transport materials for blue OLEDs.