Rong-Huei Yi

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.

By combining a rigid oxygen-bridged triarylboron acceptor with a weak carbazole-based donor to mitigate the emission red-shift of the materials, the device based on 5Cz-BO exhibits near-ultraviolet emission with the peak at 416 nm, full-width-at-half of 36 nm and CIE coordinate of (0.16, 0.03).

Abstract

Near ultraviolet (NUV) organic light-emitting diodes (OLEDs) have great advantages in the field of light excitation sources, chemical and biological sensors, etc. However, the molecular design of NUV emitters still faces the challenges of spectral broadening and red-shift. In this study, attaching weak oxygen-bridged triarylboron acceptor to weak carbazolyl donor is able to address intractable problems by weakening donor–acceptor (D–A) charge transfer. Simultaneously, sterically wrapped and modified oxygen-bridged triarylboron acceptor by bulk substituents (multiple carbazolyl) can suppress intermolecular π–π stacking through steric hindrance effect. These design strategies are able to obtain short-wavelength, narrow-band emission, and great color purity. As a result, carbazolyl derivatives xCz-BO-based (x = 2, 3, 4, 5) emitters show EL emission peaks from 406 to 422 nm in the NUV light region and small full-width at half-maximums (FWHMs) of 32–41 nm over a wide range of dopant concentrations (10–40 wt.%). The most violet Commission International de I'Eclairage (CIE) color coordinate is (0.16, 0.03). Moreover, 5Cz-BO can be employed as host for vacuum-/solution-processed blue OLEDs and these devices exhibit high performance with EQEs of over 20%.

The peripheral steric hindrance unit indolo[3,2,1-jk]carbazole enlarges the intermolecular distance and inhibits the interaction between multiple resonance thermally activated delayed fluorescence (MR-TADF) molecules. The organic light-emitting diode (OLED) exhibits a high EQE_max value of 32.9% with alleviated efficiency roll-off, which is one of the best results among the devices based on MR-TADF materials.

Abstract

The multiple resonance thermally activated delayed fluorescence (MR-TADF) materials can meet the requirement of a high color gamut of displays due to their narrowband emission. However, most reported organic light-emitting diodes (OLEDs) based on MR-TADF materials suffer from severe efficiency roll-off. Herein, three green MR-TADF emitters, p-ICz-BNCz, m-ICz-BNCz, and dm-ICz-BNCz, are obtained by introducing bulky indolo[3,2,1-jk]carbazole (ICz) units into the classical DtBuCzB skeleton at the para or meta positions relative to the boron-substituted phenyl ring. Compared with the para-substitution of ICz, the meta-substitution not only increases the reverse intersystem crossing rate constants of m-ICz-BNCz and dm-ICz-BNCz by nearly three times, but also makes their configurations more twisted. The two factors work together to improve the utilization of triplet excitons of the emitters, showing photoluminescence quantum yields exceeding 90%. As a result, the two corresponding OLEDs exhibit maximum external quantum efficiency (EQE_max) values of 28% and 32.9%, respectively, with low-efficiency roll-off. At the high brightness of 1000 cd m⁻², the EQE values of the two devices still maintain at 19.3% and 25.0%, respectively. In addition, green emissions with Commission Internationale de l'Eclairage coordinates of (0.20, 0.70) and (0.30, 0.67) are also observed.

Two novel functionalized tetradentate-ligand-based Pt(II) complexes are prepared and applied as blue phosphorescent emitters in OLED devices. The devices exhibit low turn-on voltages and outstanding efficiencies with clear blue electroliuminescence.

Abstract

Efficient, electrochemically stable blue phosphors are essential for advancing the organic light-emitting diode (OLED) industry. Specifically, the characteristics of these phosphors must be further refined to realize commercially viable OLED devices with high stability, efficiency, and color purity. To that end, a new simple molecular design approach is devised in this study for synthesizing tetradentate-ligand-based Pt(II) complexes exhibiting intense blue emission. Essentially, novel Pt(II) complexes Pt3 and Pt4 are prepared by introducing the tert-butyl and cyano groups to the ligand of previously reported highly stable, efficient Pt(II) complexes for preventing molecular aggregation and regulating the frontier levels, respectively, and then fully characterized. Both complexes display a blue emission band in solution and solid states with remarkably low full-width-at-half-maximum values. Additionally, multilayer phosphorescent OLEDs are fabricated using Pt3 or Pt4 as emitters and SiCzCz/SiTrzCz2 as a mixed-host system. The devices demonstrate outstanding performance parameters, such as higher efficiencies than those of the devices containing the previously reported Pt(II) complexes and good color purity (CIEy ≈ 0.18). These findings suggest that the molecular design approach employed in this study for creating tetradentate-ligand-based Pt(II) blue phosphors is effective and can potentially expedite the commercialization of blue phosphorescent emitters in the OLED industry.

This article presents novel pyrene-based aggregation-induced emission luminogens (AIEgens) with broad color-tuning emission from deep blue to orange-red, via tuning the electronic effect of the π-bridge linkers. The selected blue, green, and orange-red pyrene-based AIEgens are utilized as fluorescent ink for Chinese characters and fine arts writing, with a vivid artistic display.

Abstract

A molecular design strategy for the precise regulation of full-color-tunable emission organic luminescence materials is not yet systematically established for pyrene chemistry. To fabricate color-tunable and highly-efficiency pyrene-based emitters, this article presents novel pyrene-based molecules with donating-π-accepting structures, which exhibit bright, relatively narrow-band FWHM emission, broad color-tunable from deep blue (439 nm) to orange-red (599 nm) both in solution and in the solid state. Moreover, the compounds 2a, 2d–g exhibit typical aggregation-induced emission (AIE) characteristics, with an enhanced fluorescence quantum yield in the solid state. The experimental results indicated that the presence of the sterically bulky meta-substituted biphenyl adopts an out-of-plane twist conformation, which can strengthen the rigidity of the molecular conformation and suppress the intermolecular π–π stacking in the aggregated state, resulting in an enhanced emission in the solid state. The prepared pyrene-based AIEgens are applied as fluorescent inks to write Chinese characters and art with a vivid pattern. Thus, this article not only presents an efficient molecular strategy to construct pyrene-based AIEgen with broad color-tunable emission properties for practical applications, but also display a powerful combination of the strong alliance between the advanced luminescent materials, art and Chinese traditional culture.

A sort of host and guest materials which can consume triplet oxygen obviously are designed and synthesized based on triphenylamine and diphenyl phosphine oxygen groups. They can be fabricated into amorphous doping systems or co-doped with PMMA to achieve a precisely controlled photoactivation process, realizing oxygen detection and activation time-lifetime dual-resolved display.

Abstract

The photo-active ultralong organic phosphorescence (UOP) materials can only emit UOP gradually under consistent UV irradiation, which is primarily attributed to internal quenching of triplet oxygen, yet manipulating the rate of the photo-activating process is seldom reported. In addition, amorphous small-molecule doping UOP material is rarely reported either. In this study, a series of host and guest materials are synthesized and doped into amorphous UOP doping systems. These doping systems demonstrated a tunable photo-activating rate (4–6 seconds to reach a saturated state), and the amorphous structure realized the sensitive detection of oxygen. The results affirm that triplet oxygen plays a pivotal role in determining whether UOP can be emitted, and importantly, it is established that a crystalline structure in small-molecular doping systems is not a necessary condition. Furthermore, polymer-based UOP materials, manufactured through co-doping with both host and guest, exhibited tunable photo-activating rates (4–16 s) and lifetimes (226.38–462.78 ms). To expand the application, the UV-curing resin-based UOP materials are prepared via 3D-printing technology. This innovative work introduces a new approach for applying UOP materials in the field of amorphous doping system, providing a guiding strategy for widespread applications in oxygen detecting, time-resolved information display and dynamic multi-dimensional anti-counterfeiting.

Narrowband light-emitting electrochemical cells (LECs) are fabricated with ionic multi-resonance thermally- activated delayed fluorescence (TADF) guest emitters, which show high external quantum efficiencies (EQEs) up to 13.0% under constant-voltage driving and peak brightness/EQE/half-lifetime at 780 cd m⁻²/5.6%/62.2 h under constant-current driving. A half-lifetime of ≈630 h is further achieved at 136 cd m⁻².

Abstract

The development of efficient, bright, and stable narrowband light-emitting electrochemical cells (LECs) has remained a challenge. Here, intrinsically ionic multi-resonance thermally activated delayed fluorescence (MR-TADF) emitters are reported as guest emitters for narrowband LECs, which are developed by attaching an imidazolium cation onto a typical MR-TADF emitter. In solution, the emitters show green–blue emission peaked at 486−497 nm with small full widths at half-maximum (FWHMs) at 24−26 nm. In doped films, they show narrowband green–blue emission with high luminescent efficiencies at ≈90%. LECs using an ionic exciplex host and the ionic MR-TADF guest emitters show green–blue emission peaked at 494−503 nm with small FWHMs at 31−34 nm, and afford high external quantum efficiencies (EQEs) up to 10% under constant-voltage driving. With ionic TADF small-molecule hosts, the narrowband LECs show high EQEs up to 13.0% under constant-voltage driving, which is the highest among all reported narrowband LECs, and afford peak brightness/EQE/half lifetime at 780 cd m⁻²/5.6%/62.2 h under constant-current driving. A long half-lifetime of ≈630 h has further been achieved at 136 cd m⁻². The work demonstrates the great potential for the use of intrinsically ionic MR-TADF guest emitters and ionic TADF hosts to develop efficient, bright, and stable narrowband LECs.

As a result, the device fabricated by MR-TADF compound ν-DABNA-O-Me hosted by Bz2cbz has attained a blue index that goes up to as high as 253, and better device performance in terms of EQE _max, CE _max, PE _max, and blue index compared to those using mCBP and mCP as the host materials.

Abstract

The new host materials are reported to boost the multiple resonance-induced thermally activated delayed fluorescence (MR-TADF) based pure deep-blue organic light emitting diodes (OLEDs) toward further shortening the emission full width at the half maximum (FWHM). Based on an unusual asymmetric design concept, two new host compounds Bz2cb and Bz2cbz are synthesized. Despite possessing a compact and rigid molecular packing in crystal, Bz2cbz shows pure amorphous morphology via vapor deposition, as confirmed by the grazing-incidence wide-angle X-ray scattering (GIWAXS) analysis. Via incorporating a promising MR-TADF emitter, ν-DABNA-O-Me, into Bz2cb and Bz2cbz films, highly pure deep-blue OLEDs are successfully demonstrated. Remarkably, the Bz2cbz device exhibits a 464 nm electroluminescence (EL) with narrow FWHM of 22 nm, accompanied by the reduction of the 0–1 vibronic sideband, and a maximum external quantum efficiency (EQE _max) of 28.2%, which, overall, reaches the true-blue Commission Internationale de l'Eclairage coordinates (CIE) of (0.13, 0.07) and the high blue index of 253. The amorphous film formation turns out to be an important factor that is previously unrecognized to externally fine-tune the MR-TADF OLEDs toward even higher color purity.

A high-performance single-cell all-fluorescent color-tunable white device with a single-doped single-emissive-layer structure is achieved by using a multi-functional deep-blue hybrid local and charge transfer fluorophore as an emitter as well as a universal host for the yellow thermally activated delayed fluorescence emitter, realizing a record-breaking power efficiency of 89.50 lm W^‒1 and a large correlated color temperature span from 3749 to 18 279 K.

Abstract

It is a vitally important and challenging task to achieve high efficiency and wide color-tunable white organic light emitting diodes (CT-WOLEDs) meeting the needs of various decoration and lighting applications. Here, a high-performance single-cell all-fluorescent CT-WOLED with a single-doped single-emissive-layer structure has been developed employing a multi-functional hybrid local and charge transfer (HLCT) fluorophore 2-(4-(9H-carbazol-9-yl)−2′,5′-difluoro-[1,1′:4′,1′'-terphenyl]−4-yl)−1-phenyl-1H-phenanthro[9,10-d]imidazole (PICZ2F) as a deep-blue emitter as well as an effective host for a yellow thermally activated delayed fluorescence emitter. The record-breaking power efficiency of 89.50 lm W^‒1 and correlated color temperature (CCT) span from 3749 to 18 279 K are achieved simultaneously, which is not only one of the state-of-the-art CT-WOLEDs reported so far, but also comparable to the best values from all-fluorescent white devices with a single-emissive-layer. Moreover, by using PICZ2F as an emitter, an external quantum efficiency (EQE) of 7.10% with the Commission Internationale de lEclairage (CIE) coordinates of (0.155, 0.068) is achieved in the doped device, and a low-efficiency roll-off even at a high luminance of 15 000 cd m⁻² (EQE₁₅₀₀₀: 5.80%) is achieved in the non-doped device. Overall, the findings provide a promising strategy to develop simple but efficient CT-WOLEDs.

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.

The weak hybridization of S₁ and S₂ excited state is investigated in a novel blue-emissive material TDFBO. The “hot-exciton” mechanism is revealed by the triplet-related, millisecond-lifetime. As a result, TDFBO gives high performances on electron mobility (3.57×10⁻⁴ cm²·V⁻¹·s⁻¹), doped OLED (EQE_max = 11.1%) and photoinitiation for acrylate monomer.

Abstract

Herein this work, a novel donor-π-acceptor (D-π-A) pure-blue hybrid local and charge-transfer (HLCT) fluorescent material TDFBO and its functionalization as organic light emitting diode (OLED) emitter and photoinitiator (PI) in photopolymerization is reported. The weak-hybridization property involved by the fluorene π-bridge can simultaneously give satisfied photo-luminescent quantum yield (PLQY) and make efficient “hot-exciton” channel achievable. Moreover, the D-π-A structure can also promote an exceeding electron mobility as high as 3.57×10⁻⁴ cm² V⁻¹ s⁻¹. Finally, it is noted that the TDFBO-doped OLED can be regarded as the best one among the pure-blue emissive OLEDs, which exhibits a high maximum external quantum efficiency of 11.1%, while the rolling-off only stands on a low level, as 6% at 100 cd m⁻². Additionally, a relatively high final conversion of C = C double bond in a representative acrylate monomer is also attained by photoinitiation of TDFBO under 405 nm LED, where the photopolymerization has been applied to 3D printing.

Efficient and stable deep blue phosphorescent OLEDs are developed employing N-heterocyclic carbene (NHC)-based tetradentate Pt(II) complexes as emitters. PtON5N-dtb-based device shows narrow emission spectrum with full-width at half maximum (FWHM) of 30 nm, demonstrates a peak external quantum efficiency (EQE) of 20.4%, and achieves an estimated operational lifetime LT₉₀ of 85 h at an initial brightness of 1000 cd m⁻².

Abstract

Stable and efficient deep-blue organic light-emitting diodes (OLEDs) are in high demand for display and lighting applications but are rarely reported due to their poor operational lifetimes. Herein, the study designs and synthesizes two novel N-heterocyclic carbene (NHC)-based tetradentate Pt(II) complexes PtON5-dtb and PtON5N-dtb, and thoroughly investigate their electrochemical and photophysical properties. Functionalization of the NHC moieties can increase the metal-to-ligand charge transfer (^1/3MLCT) characters in their lowest triplet excited-states, resulting in significantly shortened photoluminescent lifetimes and remarkably improved device performance. A deep blue OLED employing PtON5N-dtb as an emitter exhibits a narrow spectral bandwidth with a full-width at half maximum (FWHM) of 30 nm and a CIE_y value of 0.17 and demonstrates a maximum external quantum efficiency (EQE) of 20.4% with a small efficiency roll-off, which maintains a high EQE of 18.5% at 1000 cd m⁻². Moreover, the deep blue OLED also realizes a long-measured operational lifetime LT₉₀ (time to 90% of the initial luminance) of 71 hours with an initial brightness of 1134 cd m⁻², corresponding to an estimated device lifetime LT₉₀ of 85 h at 1000 cd m⁻². This represented an eightfold lifetime improvement for PtON5N-dtb-based deep blue OLED compared to PtON7-dtb in the same device setting.

Z19, designed by synergistic side-chain engineering, affords binary organic solar cells (OSCs) with an impressive PCE of 19.2% at a high open-circuit voltage (V _OC), 1.002 V. This is the best performance ever reported for OSCs, V _OC > 1.0 V. Indications are that such design of organic semiconductors, considering the energy-gap law, may offer the next efficiency breakthrough in OSCs.

Abstract

Restricted by the energy-gap law, state-of-the-art organic solar cells (OSCs) exhibit relatively low open-circuit voltage (V _OC) because of large nonradiative energy losses (ΔE _nonrad). Moreover, the trade-off between V _OC and external quantum efficiency (EQE) of OSCs is more distinctive; the power conversion efficiencies (PCEs) of OSCs are still <15% with V _OCs of >1.0 V. Herein, the electronic properties and aggregation behaviors of non-fullerene acceptors (NFAs) are carefully considered and then a new NFA (Z19) is delicately designed by simultaneously introducing alkoxy and phenyl-substituted alkyl chains to the conjugated backbone. Z19 exhibits a hypochromatic-shifted absorption spectrum, high-lying lowest unoccupied molecular orbital energy level and ordered 2D packing mode. The D18:Z19-based blend film exhibits favorable phase separation with face-on dominated molecular orientation, facilitating charge transport properties. Consequently, D18:Z19 binary devices afford an exciting PCE of 19.2% with a high V _OC of 1.002 V, surpassing Y6-2O-based devices. The former is the highest PCE reported to date for OSCs with V _OCs of >1.0 V. Moreover, the ΔE _nonrad of Z19- (0.200 eV) and Y6-2O-based (0.155 eV) devices are lower than that of Y6-based (0.239 eV) devices. Indications are that the design of such NFA, considering the energy-gap law, could promote a new breakthrough in OSCs.

A narrowband pure blue MR-TADF emitter that shows record fast k _RISC on the order of 10⁶ s⁻¹ is demonstrated. The emitter maintains its high performance in an OLED, which shows an EQE_max of ≈20% and a CIE_y of 0.041, matching the Rec. BT.2020-2 color point for blue.

Abstract

Narrowband emissive multiresonant thermally activated delayed fluorescence (MR-TADF) emitters are a promising solution to achieve the current industry-targeted color standard, Rec. BT.2020-2, for blue color without using optical filters, aiming for high-efficiency organic light-emitting diodes (OLEDs). However, their long triplet lifetimes, largely affected by their slow reverse intersystem crossing rates, adversely affect device stability. In this study, a helical MR-TADF emitter (f-DOABNA) is designed and synthesized. Owing to its π-delocalized structure, f-DOABNA possesses a small singlet-triplet gap, ΔE _ST, and displays simultaneously an exceptionally faster reverse intersystem crossing rate constant, k _RISC, of up to 2 × 10⁶ s⁻¹ and a very high photoluminescence quantum yield, Φ _PL, of over 90% in both solution and doped films. The OLED with f-DOABNA as the emitter achieved a narrow deep-blue emission at 445 nm (full width at half-maximum of 24 nm) associated with Commission Internationale de l'Éclairage (CIE) coordinates of (0.150, 0.041), and showed a high maximum external quantum efficiency, EQE_max, of ≈20%.

Nature, Published online: 27 March 2024; doi:10.1038/s41586-024-07149-x

A new concept of using out-of-plane interactions, that is, spatial perturbation (SPPT), is proposed for enhancing the performance of multiple resonance thermally activated delayed fluorescence emitters. Compared to the control compound, o-BNPO with SPPT exhibits significant device efficiency improvement with maximum external quantum efficiency of up to 36.0% with reducing the roll-off, while maintaining the barely changed electroluminescence spectrum.

Abstract

For multiple resonance (MR) type thermally activated delayed fluorescence (TADF) emitters, electron cloud distributions of their π-conjugated planes are crucial for determining their eventual performance. Currently, modulation attempts of MR-TADF emitters are mainly inside the π-conjugated planes. Possible out-of-plane interactions may also significantly impact the photophysical properties, but the exploration is quite limited. Here, a novel concept of using out-of-plane (e.g., π–π and lone pair-π) interactions to introduce spatial perturbation (SPPT) to improve TADF performance is proposed. Two newly developed MR-TADF emitters, namely, o-BNPO and BNPO, which both consist of a popular MR framework, DtBuCzB, and diphenylphosphine oxide (DPPO), are compared in depth. In particular, for o-BNPO, evident π–π interaction is observed between one side of the DtBuCzB π-conjugated plane and a phenyl ring from DPPO, and lone pair-π interaction with the oxygen atom from DPPO is noticed on the other side, resulting in significantly accelerated reverse intersystem crossing and better TADF without sacrificing narrowband emission features. Ultimately, in organic light-emitting diodes with sensitizer-free emitting layers, both emitters achieve similar narrowband emissions, while the o-BNPO-based device demonstrates a much higher external quantum efficiency of 36% and milder efficiency roll-off.

Ultrafast bipolar charge transport and strong blue delayed fluorescence are realized in neat films of novel organic molecules constructed with ring-fused carbonyl-containing electron acceptors and spiro-acridine electron donors, and high-performance non-doped thin-layer OLEDs and simplified non-doped thick-layer OLEDs with record-beating EQEs of 30.2% and 23.0% and tiny roll-offs are achieved.

Abstract

Achieving strong solid-state photoluminescence and fast charge transport simultaneously for organic molecules is of significant importance but challenging because of the trade-off between these properties. Herein, two tailored blue luminescent molecules constructed with ring-fused carbonyl-containing electron acceptors and spiro-acridine electron donors are developed. Owing to ordered long-range molecular alignment with proper interaction energies, their neat films exhibit ultrafast bipolar charge transport and strong delayed fluorescence with high quantum yields and short lifetimes. In doped organic light-emitting diodes (OLEDs), both molecules display eminent electroluminescence performances with excellent external quantum efficiencies (EQEs) of 40.6%. They also exhibit brilliant blue lights with record-beating EQEs of 30.2% in non-doped thin-layer OLEDs, and more importantly, high-performance simplified non-doped thick-layer OLEDs are achieved, rendering lowered driving voltages, and the best EQEs of 23.0% with tiny efficiency roll-offs. In addition, using them as sensitizers, remarkable EQEs of 40.1% and 23.2% with ultrasmall efficiency roll-offs are realized in blue hyperfluorescence thin-layer and thick-layer OLEDs, respectively. The operational lifetimes are obviously elongated matter in non-doped thick-layer devices or hyperfluorescence thick-layer devices. This work provides promising candidates for efficient simplified thick-layer OLEDs and opens a new avenue toward organic molecules with strong delayed fluorescence and fast charge transport simultaneously.

Color-tunable dual-mode organic afterglow is achieved from the polymethyl methacrylate (PMMA) doped indolo[3,2-b]carbazole system, harvesting green one at temperature <298 K and blue one even at high temperature of 358 K. The afterglow is triggered by UV light photoactivation and composed by the persistent multi-resonance thermally activated delayed fluorescence (MRTADF) and organic ultralong room temperature phosphorescence (OURTP) simultaneously.

Abstract

Organic afterglow can be generated from persistent thermally activated delayed fluorescence (pTADF) or organic ultralong room temperature phosphorescence (OURTP), but the pTADF plus OURTP type organic afterglow is challenging to achieve, especially for the color-tunable and high-temperature ones. Herein, an accessible strategy toward such dual-mode afterglow is presented by doping the indolo[3,2-b]carbazole (ICZ-p1) into polymethyl methacrylate (PMMA). The resulting films exhibit photo-activated afterglow with two persistent emission peaks of ca. 435 and 497 nm. Impressively, their longest lifetimes respectively reach to 2.28 and 2.47 s at 298 K, along with 0.32 and 0.42 s at 360 K, enabling the afterglow at room and high temperature. Experimental and theoretical results reveal that the photo-activated afterglow is associated with the elimination of molecular O₂ inside film and composed by the pTADF with multi-resonance (MR) effect and OURTP. By altering the temperature from 77 to 358 K, the color-tunable afterglows of green and blue are harvested at such temperature ranges. Benefiting from the multi-resonance thermally activated delayed fluorescence (MRTADF) characteristics, this emitter can release narrow-band electroluminescence. Consequently, the results obtained here may offer important references for chasing MRTADF plus OURTP-type dual-mode organic afterglow showing color-tunable and high-temperature features.

Photosensitizers with D-π-A structures are constructed for photodynamic anti-tumor therapy by using multi-N heterocycle (purine) as π-bridges, which enhances D-π-A strength and extends the π-conjugation system, thus facilitating the intersysterm crossing process and realizing an excellent Type I and Type II reactive oxygen species generation efficiency.

Abstract

The efficient generation of reactive oxygen species (ROS) is crucial for the photodynamic therapy (PDT) effect. The D-π-A molecular engineering strategy can effectively separate the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) distribution to achieve a smaller energy gap thereby facilitating ROS generation of photosensitizers (PSs). Incorporating heterocycles as π-bridges can not only extend the conjugation system with improving the degree of π-delocalization but also effectively accelerate the intersystem crossing process. Herein, a N-heterocycle purine is innovatively integrated into the D-π-A structure as a π-bridge, which significantly enhances the photodynamic performance by achieving high levels of Type I and Type II ROS generation. The most potent TPM-QN2 is obtained by modulating the electron-withdrawing ability of the acceptor (quinolinium), with a ¹O₂ yield of 9.32, which is the highest yield reported to date. Furthermore, these purine-based PSs exhibit excellent capabilities in promoting cell photodynamic ablation and inhibiting tumor tissue growth. This novel approach of introducing natural heterocycles provides a promising avenue for developing high-performance PSs and promoting tumor phototherapy.