Quenching-Resistant Multiresonance TADF Emitter Realizes 40% External Quantum Efficiency in Narrowband Electroluminescence at High Doping Level

Quantum-Chemical Simulation of Multiresonance Thermally Activated Delayed Fluorescence Materials Based on B,N-Heteroarenes Using Graph Neural Networks

Multiresonance thermally activated delayed fluorescence (MR-TADF) emitters are crucial for the next generation of electroluminescent devices due to their high efficiency and narrowband emission. In this study, we developed a simple molecular design for MR-TADF materials based on a π-extended DABNA core decorated with four different framework types (carbazole (X = none), acridine (X = C(Me)2), phenoxazine (X = O), and phenothiazine (X = S)) and further modified with 18 different annulated systems. The optoelectronic properties of these compounds were modeled using density functional theory. Based on quantum chemical calculations, an accelerated search tool for MR-TADF emitters was developed using deep learning methods, enabling the prediction of energy values approximating experimental results.

Integration of Through-Space Conjugation of an Adjacent Arene with a Nitrogen/Carbonyl Framework for Narrowband Emission

Organic luminescent materials featuring noncovalent through-space conjugation (TSC) have attracted considerable attention. However, the presence of multiple vibrational energy levels and weak spatial electron delocalization typically results in broad emission peaks for TSC-based emitters, significantly impeding their extensive application in optoelectronic technologies. Herein, two TSC emitters, TSFQ-TRZ and TSFQ-Ph, were synthesized by integrating a fused nitrogen/carbonyl skeleton with various adjacent arene 2,4,6-triphenyl-1,3,5-triazine (TPTRZ) and phenyl group segments through a rigid spiro spacer. These emitters exhibited narrow emissions, with full widths at half-maximum of 19 nm and 25 nm, respectively. Experimental and theoretical investigations unveiled that the TPTRZ segment introduces steric hindrance, while simultaneously suppressing molecular vibrations through intramolecular interactions-a key factor in achieving narrow emissions. Leveraging this narrow blue emission, electroluminescent devices employing TSFQ-TRZ as the emitter achieved an impressive maximum external quantum efficiency of 26.7 %, which further increased to 28.3 % when sensitized by phosphorescent emitter. This work demonstrates highly efficient, narrowband emissions from TSC-based emitters, thereby expanding their potential applications in the electroluminescence field.

Extending Frontier Molecular Orbitals Delocalization via Donor Fusion: Construct Long-Wavelength Twisted Multiple Resonance Emitters with Efficient Narrowband Emission

Multiple resonance thermally activated delayed fluorescence (MR-TADF) emitters are promising candidates for ultra-high-definition organic light-emitting diodes (OLEDs) displays. Here, we propose a general strategy for post-functionalizing MR core, introducing donors on the lowest unoccupied molecular orbital (LUMO) position via Suzuki coupling and then fusing the donors to the highest occupied molecular orbital (HOMO) position via Scholl cyclization, which can extend frontier molecular orbitals delocalization to construct long-wavelength narrowband emitters. Two proof-of-concept molecules, BN-PhAzCz and BN-tCzAzPh, are constructed, achieving large spectral red-shifts while maintaining narrowband emission. The distorted configuration resulting from the hetero[6]helicene structure introduces twisted π-π* transition, which effectively enhances spinorbit coupling, ultimately enabling molecule BN-PhAzCz to achieve a fast reverse intersystem crossing rate (kRISC = 6.4 × 104 s-1). BN-PhAzCz-based single-host OLED exhibits green emission at 528 nm with Commission Internationale de L'Eclairage (CIE) coordinates of (0.26, 0.69) and maximum external quantum efficiency (EQE) of 38.2% with efficiency roll-off of 28.0% at 1000 cd m-2 under 5 wt% doping concentration. Even at 20 wt% doping concentration, the maximum EQE remains at 29.6% with little change in the spectral profile.

Through-Space Interactions Enable Aggregation-Induced Quenching Suppression and Spin-Flipping Enhancement of Carbonyl-Nitrogen-Based Multiple Resonance Thermally Activated Delayed Fluorescence Emitters

Multiple resonance (MR) thermally activated delayed fluorescence (TADF) materials hold significant potential for applications in high color purity and highly efficient organic light-emitting diodes (OLEDs). However, their inherently large planar structures often result in severe aggregation-induced quenching and slow spin-flip processes, presenting significant challenges that limit their practical applications. In this study, we designed and synthesized two MR-TADF molecules, tCON-Cz and tCON-2tBuCz, by incorporating a tCON backbone with carbazole or 3,6-di-tert-butylcarbazole at the ortho position of the phenyl ring. This strategic design introduces a highly twisted three-dimensional structure, effectively mitigating aggregation-induced quenching. Additionally, it creates a through-space charge transfer channel that facilitates reverse intersystem crossing, thereby enhancing TADF efficiency. As a result, both molecules exhibit high photoluminescence quantum yields. When incorporated into devices, these OLEDs demonstrated remarkable performance, achieving high external quantum efficiencies of 23.70% for tCON-Cz and 22.84% for tCON-2tBuCz at doping concentrations as high as 20%. Notably, both devices retained the narrow full width at half-maximum of around 36 nm, consistent with the parent tCON skeleton, ensuring superior color purity.

Azepination-Induced Frontier Molecular Orbital Delocalization of Multiple Resonance Emitters: Constructing Highly Efficient Narrowband Electroluminescent Materials

Developing diversified construction strategies for high-color-purity and efficient multiple resonance thermally activated delayed fluorescence (MR-TADF) materials is a major strategic demand to meet the requirements of ultra-high-definition organic light-emitting diode (OLED) displays, posing a significant challenge to the design and synthesis of emitters at the molecular level. Herein, a strategy is proposed for azepination-induced frontier molecular orbital (FMO) delocalization of MR emitters, that is, embedding azepine into the prototype molecule BNCz can effectively improve the π-conjugation degree and extend the FMO delocalization, thereby constructing a series of long-wavelength MR-TADF materials with narrowband emission. Through an intramolecular Scholl reaction, these target molecules with an azepine-embedded core are afforded by one-fold heptagonal cyclization of BNCz core and the phenyl ring attached to (aromatic amine-substituted) aryl precursor. They all exhibit efficient green emission around 520 nm and narrow full-widths at half-maximum (FWHMs) of ≤ 37 nm in toluene. OLEDs employing these emitters show excellent electroluminescence (EL) performances, among which m-PAz-BNCz-based OLED exhibits the optimal EL performances with a peak of 528 nm, a FWHM of 37 nm, Commission Internationale de L'Eclairage (CIE) coordinates of (0.26, 0.70), and a maximum external quantum efficiency (EQE) of 36.2%.

Toward Intrinsically Stretchable OLEDs with High Efficiency

Wearable electronics require stretchable displays that can withstand large and repeated mechanical deformation without failure. Intrinsically stretchable organic light-emitting diodes (ISOLEDs) that operate under DC voltage provide promising candidates for wearable display applications. However, the lack of sophisticated stretchable materials and processing techniques suitable for ISOLEDs results in a significant deficit in the efficiency of state-of-the-art ISOLEDs compared to industrial standards. The design of stretchable conducting and semiconducting materials poses a significant challenge because of trade-off relationships between stretchability and properties such as conductivity and charge carrier mobility. To increase the efficiency of ISOLEDs to meet industrial standards, strategies to overcome these trade-offs must be developed. This perspective discusses recent progress and challenges in designing stretchable electrodes, light-emitting materials, transport materials, and potential applications of ISOLEDs. It provides a useful guide in this field to develop efficient ISOLEDs for system-level integration.

Spectral Narrowing Strategies in Multiple Resonance Thermally Activated Delayed Fluorescence Materials

Multi-resonance thermally activated delayed fluorescence (MR-TADF) materials possess unique advantages of high-efficiency and narrowband emission, which have rapidly occupied an important position in the field of organic light-emitting diodes (OLEDs). In recent years, significant advancements have been made in the development of MR-TADF materials, particularly in achieving spectral narrowing for high-color-purity OLED applications. Based on diverse MR-TADF molecular skeletons, this review summarizes the primary molecular strategies to narrow spectrum by suppressing structural relaxation and intermolecular interactions. Key strategies include π-conjugation extension, increased molecular rigidity, and the introduction of bulky substituents and intramolecular hydrogen bonds. Additionally, effects of these strategies on photophysical properties are discussed. These molecular design strategies are expected to offer valuable insights for the future design of high-efficiency, narrowband OLED emitters.

Engineering Nitrogen/Carbonyl MR-TADF Emitters: Spiro-Lock and Tert-Butyl Synergy in Narrowband Blue Emission

Multi-resonance thermally activated delayed fluorescence (MR-TADF) emitters with rigid planar structures are promising for their exceptional color purity and outstanding device efficiency. However, as an important MR unit, rigidly interlocked nitrogen/carbonyl-based blue materials often face challenges like spectral broadening, red-shifting, and reduced efficiency compared to nitrogen/boron system. Herein, a peripheral modification strategy incorporating tert-butyl groups via a spiro-lock framework is used to synthesize four molecules: QAO-TF, TQAO-TF, TQAO-F, and TSOQ. The spiro-lock structure solidifies the molecular framework, narrows the emission bandwidth, and elevates the photoluminescence quantum yield to over 96%. Meanwhile, the peripheral tert-butyl groups introduce steric hindrance, isolating the luminescent core and suppressing intermolecular interactions in the solid state, thereby improving device efficiency while maintaining narrowband emission. Notably, TQAO-F shows an electroluminescence peak at 476 nm with a 25 nm full width at half maximum (FWHM) and an external quantum efficiency (EQE) of 31.7%. TSOQ, with its oxygen-induced charge effect, achieves narrowband pure blue emission with an FWHM of 20 nm, surpassing 30% EQE without sensitizers. This overall performance suggests its potential to rival the classic nitrogen/boron system.

Synergetic Multiple Charge-Transfer Excited States for Anti-Quenching and Rapid Spin-Flip Multi-Resonance Thermally Activated Delayed Fluorescence Emitter

The development of multiple resonances thermally activated delayed fluorescence (MR-TADF) emitters exhibiting high efficiency, narrowband emission, rapid reverse intersystem crossing rate (kRISC), and suppressed concentration quenching simultaneously is of great significance yet a formidable challenge. Herein, an effective strategy is presented to realize the above target by synergizing multiple charge-transfer excited states, including short-range charge transfer (SRCT), through-bond charge transfer (TBCT), and through-space charge transfer (TSCT). The proof-of-concept emitter 4tCz2B exhibits a bright green emission with a narrow full width at half maximum (FWHM) of 21 nm (0.10 eV) in solution, high photoluminescence quantum yield of 97%, fast kRISC of 7.8 × 105 s-1 and significantly suppressed concentration quenching in film state. As a result, the sensitizer-free organic light-emitting diodes (OLEDs) achieve maximum external quantum efficiencies (EQEmaxS) of over 34.5% together with an unaltered emission peak at 508 nm and FWHM of 26 nm at doping concentrations ranging from 3 to 20 wt.%. Even at a doping ratio of 50 wt.%, EQEmax is still as high as 25.5%. More importantly, the non-sensitized devices exhibit significantly reduced efficiency roll-offs, with a minimum value of 13.4% at a brightness of 1000 cd m-2.

Excited-State and Steric Hindrances Engineering Enable Fast Spin-Flip Narrowband Thermally Activated Delayed Fluorescence Emitters with Enhanced Quenching Resistance

Multi-resonance thermally activated delayed fluorescence (MR-TADF) materials have great potential for applications in ultrahigh-definition (UHD) organic light-emitting diode (OLED) displays, that benefit from their narrowband emission characteristic. However, key challenges such as aggregation-caused quenching (ACQ) effect and slow triplet-to-singlet spin-flip process, especially for blue MR-TADF materials, continue to impede their development due to planar skeletons and relatively large ΔESTs. Here, an effective strategy that incorporates multiple carbazole donors into the parent MR moieties is proposed, synergistically engineering their excited states and steric hindrances to enhance both the spin-flip process and quenching resistance. As expected, the designed materials namely 5Cz-BNO and 5Cz-BN exhibit bright blue and green emissions with narrow full-width at half-maximums (FWHMs) around 23 nm, together with significantly improved reverse intersystem crossing (RISC) rates. The OLEDs based on 5Cz-BNO and 5Cz-BN with doping concentrations from 5 to 20 wt % achieve high maximum external quantum efficiency (EQEmax) values exceeding 30 % with suppressed efficiency roll-offs and improved operational stability. This work offers an effective approach for designing doping-insensitive blue and green MR-TADF materials with fast spin-flip processes by integrating the engineering of excited states and steric hindrances.

Pressure-Induced Emission Enhancement of Multi-Resonance o-Carborane Derivatives via Exciton‒Vibration Coupling Suppression

Polycyclic multiple resonance (MR) molecules reveal narrowband emission, making them very promising emitters for high color purity display. Nevertheless, they still have challenges such as aggregation-induced emission quenching and spectral broadening. Overcoming these obstacles requires an in-depth understanding of the correlations among the alterations in their geometries, packing structures, and molecular vibrations and their corresponding changes in their photoluminescence (PL) properties. Herein, it is demonstrated that high-pressure infrared, UV-visible absorption, and fluorescence spectroscopies can be combined with computational results to elucidate the influence of the subtle structural variations on the exciton‒vibration couplings and their PL properties. An ortho-carborane-decorated MR emitter (BNC) is a piezochromic molecule and exhibits emission enhancement under high pressure. A thorough analysis of the in situ experimental measurements and calculated results reveals that the pressure-induced changes in the exciton binding energy and exciton‒vibration couplings are responsible for the unusual piezochromism. This research provides insights into the structure‒fluorescence relationship and potential for high-pressure techniques to optimize MR materials for advanced organic light-emitting diodes (OLEDs) applications.

A mesityl-functionalized double-boron-nitrogen-oxygen-embedded multi-resonance framework achieves anti-quenching narrowband deep-blue electroluminescence with EQE over 30% and CIE y of 0.046

Developing highly efficient deep-blue multi-resonance thermal activated delayed fluorescence (MR-TADF) materials for ultra-high-definition organic light-emitting diodes (OLEDs) displays that meet the stringent BT.2020 standard remains a significant challenge. In this study, we present a strategy to achieve high-performance deep-blue MR-TADF emitters by integrating a large π-conjugated double-boron-embedded MR skeleton with strategically positioned peripheral steric hindrance groups. The developed molecule, DMBNO, exhibits a narrow full-width at half maximum (FWHM) of 19 nm, with a deep-blue emission peak at 444 nm in diluted toluene solutions. Additionally, it achieves high photoluminescence quantum yield (PLQY) and a horizontal ratio of emitting dipole orientation (θ ∥) exceeding 90% in doped films. Notably, DMBNO demonstrates anti-quenching properties and effectively suppresses spectrum broadening. Consequently, OLEDs based on DMBNO achieve a high maximum external quantum efficiency (EQEmax) of 32.3%, with an impressive Commission Internationale de l'Eclairage (CIE) y-coordinate of 0.046, fully satisfying the BT.2020 blue gamut at a high doping concentration of 10 wt%. These findings offer valuable insights into molecular design tactics for deep-blue MR-TADF emitters featuring high efficiency, ultra-pure color, and anti-quenching characteristics.

Enabling High-Performance Multi-Resonant TADF Emitters via Intramolecular Hydrogen Bond

Hydrogen bonds (HBs), prevalent strong interactions in organic compounds, can effectively constrain single bond rotation, leading to rigid planar configurations. This rigidity enhances emission efficiency and narrows the emission spectrum of luminescent materials. Recent advances have leveraged HBs to advance high-performance donor-acceptor thermally activated delayed fluorescence (TADF) materials. However, their application in multi-resonance (MR) TADF emitters remains limited. We herein developed MR-TADF emitters incorporating intramolecular hydrogen bonds (IHBs) with pyrimidine as the HB acceptor. The rigid planar conformation induced by IHBs significantly improved photoluminescence quantum yield, extended emission wavelength, reduced full-width at half-maximum, and decreased non-radiative decay rates for BN-2Pm compared to BN-5Pm. Devices based on BN-2Pm achieved a maximum external quantum efficiency of 36.5 %, a current efficiency of 102.3 cd A-1, a power efficiency of 84.6 lm W-1, and Commission Internationale de l'Éclairage (CIE) coordinates of (0.18, 0.71). In contrast, BN-5Pm exhibited lower values: 14.6 %, 36.8 cd A-1, 27.6 lm W-1, and (0.12, 0.57), respectively.

Improving the Blue Color Purity of Tetradentate Pt(II) Complexes with the Assistance of F⋅⋅⋅H Interaction towards High-Performance Blue Phosphorescent OLEDs with EQE over 33

Among the various challenges in the field of organic light-emitting diodes (OLEDs), simultaneously achieving high efficiency, a long lifespan, and a narrow full-width at half maximum (FWHM) in blue OLEDs remains a significant hurdle. Herein, we demonstrate a strategy to improve the color purity of tetradentate Pt(II) complexes with the assistance of ⋅⋅⋅H interaction by incorporating trifluoromethyl (-CF3) groups into the well-known blue tetradentate Pt(II) phosphorescent complex. The results show that the different substitution positions of -CF3 have significantly varying effects on the FWHM values of the complexes; specifically, introducing -CF3 on the benzene ring of carbazole effectively reduces the FWHM, while introducing it on the benzene ring linked to the carbene unit has a minimal impact. When utilized in a mixed host system of SiCzCz/SiTrzCz2, the OLEDs with these new complexes as emitters demonstrated maximum external quantum efficiencies (EQEs) of 27.1 %, 33.8 %, and 27.6 % for PtON-CF3-1, PtON-CF3-2, and PtON-2CF3, respectively, with excellent color purity (CIEy≈0.14 for the PtON-CF3-2 based device). Notably, the device based on PtON-CF3-2 matched the stability of the benchmark PtON-TBBI complex.This work offers an important guideline for the design of high efficient Pt(II) phosphorescent complexes with good blue color purity.

A Novel Matrix-Free Hyperfluorescent System Based on Anti-Quenching TADF Host for High Color Purity MR-TADF Emitters

Organic light-emitting diodes (OLEDs) based on hyperfluorescent system have attracted widespread attention due to their ability to simultaneously achieve improvements in efficiency, lifetime, and color purity by combining the advantages of high exciton utilization sensitizers and high-color purity emitters. Traditional hyperfluorescent systems typically involve three or four components and are severely sensitive to the doping concentration (≈0.5 wt%) of a terminal emitter, which inevitably causes high costs and difficulties in reproducibility. Here, a novel design concept for a matrix-free hyperfluorescent (MFHF) system that employs a combination of an anti-quenching TADF host and a high color purity MR-TADF emitter is proposed. This strategy allows traditional concentration-sensitive MR-TADF emitters to significantly improve exciton utilization and reduce exciton lifetime at high doping levels, without the need for complex molecular modifications. The OLEDs with binary emissive layer achieve pure-green emission, a maximum external quantum efficiency of over 30%, and a high maximum power efficiency of 145 lm W-1. The approach offers a straightforward and universal method to achieve anti-quenching matrix-free hyperfluorescent OLEDs with high color purity, making them promising for commercial applications in low-cost ultra-high-definition (UHD) displays.

Precise Regulation of the Reverse Intersystem Crossing Pathway by Hybridized Long-Short Axis Strategy for High-Performance Multi-Resonance TADF Emitters

Multi-resonance thermally activated delayed fluorescence (MR-TADF) molecules have experienced great success in organic light-emitting diodes (OLEDs) owing to their outstanding quantum efficiencies and narrow full width at half-maximums (FWHMs). However, the reverse intersystem crossing (RISC) rates of MR-TADF emitters are usually small, which will lead to relatively long triplet exciton lifetime and severe efficiency roll-off. Here, we report an effective molecular design strategy to introduce multichannel RISC pathways and thus increase RISC rates without compromising the color fidelity and emission efficiency by the "hybridized long-short axis (HLSA)" strategy. The TPA-CN-BN shows a near-unity photoluminescence quantum yield, rapid RISC rate of 1.4×105 s-1, narrow FWHM of 23 nm, and small singlet-triplet energy gap (ΔEST) of 0.06 eV in solution. The non-sensitized OLED based on TPA-CN-BN exhibits a narrowband emission with the FWHM of 31 nm, in company with external quantum efficiency (EQE) of 37.9 %. Notably, the device exhibits the low efficiency roll-off as the EQEs maintain 34.8 % and 21.8 % at 100 and 1000 cd m-2, respectively, representing the best performance for single-host OLEDs based on the BCzBN skeleton. This study provides a fresh and promising approach to realize high-performance OLEDs with high color purity and remarkable device efficiency.

Pendant engineering in multiple-resonance thermally activated delayed fluorescence to yield charge-transfer and locally excited-state characteristics

Multiple-resonance thermally activated delayed fluorescence (MR-TADF) materials can exhibit narrow-spectrum characteristics owing to the inhibition of rotation within the molecules. However, the excited states of these MR-TADF materials, which influence the spin-orbit couplings (SOCs) and device efficiencies of organic light-emitting diodes (OLEDs), have not been investigated to date. In this study, we synthesized MR-TADF materials tDABNA-TP, tDABNA-DN, and tDABNA-DOB by incorporating characteristic neutral, donor, and acceptor pendants into 2,12-di-tert-butyl-5,9-bis(4-(tert-butyl)phenyl)-5,9-dihydro-5,9-diaza-13b-boranaphtho[3,2,1-de]anthracene (tDABNA). To determine the effect of pendant engineering, we investigated the excited states of the MR-TADF materials, including their singlet and triplet excited states, calculated the SOCs for their optimal reverse intersystem crossing pathways, and determined their maximum external quantum efficiencies (EQEmax) in OLEDs. The OLED with the emitter bearing the neutral pendant (tDABNA-TP) exhibited the highest EQEmax of 20.7% among those with the emitters bearing the donor (16.6%) and acceptor (12.4%) pendants, with a narrow emission range of 472-492 nm. Furthermore, the device with the tDABNA-TP emitter exhibited an operating lifetime of 196 h, which was 1.42- and 1.92-fold longer than those of the devices with the tDABNA-DN and tDABNA-DOB emitters, respectively. Our findings will promote research on the pendant engineering of MR-TADF-based OLEDs.

Conformational Modulation of Efficient Macrocyclic Emitters Featuring Delayed Fluorescence by Conjugation Length and Cavity Dimensions

The π-conjugated macrocyclic emitters with thermally activated delayed fluorescence (TADF) characteristics have attracted widespread attention in the field of organic electroluminescence (EL) materials due to their unique geometries and excellent luminescence performance. Despite the significant impact of conjugation length and cavity dimensions on molecular conformation, the influence of these factors on the excited-state properties remains understudied. Herein, we formulated a strategy aimed at modulating the conformation of TADF macrocyclic molecules containing aniline as the donor (D) unit, and triazine as the acceptor (A), linked in D-A and D-π-A alternative macrocyclic construction (MC-TNT and MC-TST). Corroborated by experimental and theoretical analyses, the compact and conformationally twisted MC-TNT exhibits efficient blue luminescence in crystalline state, facilitating EL at high doping concentrations with maximum external quantum efficiency (EQEmax) of 13.9 %, leading the field of blue macrocyclic emitters. Notably, MC-TST with π-bridge and flat conformation, demonstrates diminished Coulombic repulsion, achieving nearly 100 % photoluminescence quantum yield and superior horizontal dipole orientation of 85 % in 5 wt % doped films, and the corresponding device's EQEmax reaches record-high 32.7 % within the TADF macrocyclic domain.

Biomimetic Chlorosomes: Oxygen-Independent Photocatalytic Nanoreactors for Efficient Combination Photoimmunotherapy

Photocatalytic therapy for hypoxic tumors often suffers from inefficiencies due to its dependence on oxygen and the risk of uncontrolled activation. Inspired by the oxygen-independent and precisely regulated photocatalytic functions of natural light-harvesting chlorosomes, chlorosome-mimetic nanoreactors, termed Ru-Chlos, are engineered by confining the aggregation of photosensitive ruthenium-polypyridyl-silane monomers. These Ru-Chlos exhibit markedly enhanced photocatalytic performance compared to their monomeric counterparts under acidic conditions, while notably bypassing the consumption of oxygen or hydrogen peroxide. The photocatalytic activity of Ru-Chlos is finely tunable through light-responsive disassembly of the Ru-bridged matrix, with tunability governed by pre-irradiation duration. Utilization of Ru-Chlos loading prodrug [2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)] (ABTS) for phototherapy facilitates the generation of toxic radicals (oxABTS) and the photocatalytic conversion of endogenous NADH to NAD+, inducing oxidative stress in hypoxic cancer cells. Simultaneously, the light-responsive degradation of Ru-Chlos produces Ru-based toxins that further contribute to the therapeutic effect. This dual-action mechanism elicits potent immunogenic cell death effects and significantly enhances antitumor efficacy with the aid of a PD-l blockade. These biomimetic chlorosomes highlight their potential to advance oxygen-independent photocatalytic nanoreactors with controlled activity for novel cancer photoimmunotherapy strategies.

The Golden Age of Thermally Activated Delayed Fluorescence Materials: Design and Exploitation

Since the seminal report by Adachi and co-workers in 2012, there has been a veritable explosion of interest in the design of thermally activated delayed fluorescence (TADF) compounds, particularly as emitters for organic light-emitting diodes (OLEDs). With rapid advancements and innovation in materials design, the efficiencies of TADF OLEDs for each of the primary color points as well as for white devices now rival those of state-of-the-art phosphorescent emitters. Beyond electroluminescent devices, TADF compounds have also found increasing utility and applications in numerous related fields, from photocatalysis, to sensing, to imaging and beyond. Following from our previous review in 2017 ( Adv. Mater. 2017, 1605444), we here comprehensively document subsequent advances made in TADF materials design and their uses from 2017-2022. Correlations highlighted between structure and properties as well as detailed comparisons and analyses should assist future TADF materials development. The necessarily broadened breadth and scope of this review attests to the bustling activity in this field. We note that the rapidly expanding and accelerating research activity in TADF material development is indicative of a field that has reached adolescence, with an exciting maturity still yet to come.

Spiral-Locking Strategy for Efficient Narrowband Multiple Resonance Thermally Activated Delayed Fluorescence Emitters

Multiple resonance thermally activated delayed fluorescence (MR-TADF) materials are applied in organic light-emitting diodes (OLEDs) due to their high efficiency and color purity. However, the inherent planar structure of MR emitters presents significant challenges, including concentration-induced emission quenching, spectral redshift and broadening. To address these issues, two orthorhombic asymmetric conformational materials, SBNO and SBNOS, have been developed. Both MR-TADF emitters incorporate a sterically hindered spiro-carbon bridge to minimize intermolecular chromophore interactions. Consequently, the spectra of the SBNOS-based devices exhibit only a 4 nm redshift and a 7 nm broadening of the full-width at half maximum (FWHM) across a doping ratio range of 1-100 wt%. The steric effect produces pure green OLEDs with a CIE y of 0.69 and enhances performance, achieving a maximum external quantum efficiency (EQEmax) of up to 32.7%. The referent BNO without spiro skeleton suffers from serious spectral redshift and broadening as well as a lower device efficiency. This research demonstrates a promising approach to developing MR-TADF devices that resist redshift and broadening while maintaining high color purity and efficiency.

The Combination of a Donor-Acceptor TADF and a MR-TADF Emitting Core Results in Outstanding Electroluminescence Performance

Here the utility and potential of an emitter design are demonstrated, consisting of a narrowband-emitting multiresonant thermally activated delayed fluorescent (MR-TADF) core that is decorated with a suitably higher energy donor-acceptor TADF moiety. Not only does this D-A TADF group offer additional channels for triplet exciton harvesting and confers faster reverse intersystem crossing (RISC) kinetics but it also acts as a steric shield, insulating the emissive MR-TADF core from aggregation-caused quenching. Two emitters, DtCzBN-CNBT1 and DtCzBN-CNBT2, demonstrate enhanced photophysical properties leading to outstanding performance of the organic light-emitting diodes (OLEDs). DtCzBN-CNBT2, containing a D-A TADF moiety, has a faster kRISC (1.1 × 105 s-1) and higher photoluminescence quantum yield (ΦPL: 97%) compared to DtCzBN-CNBT1 (0.2 × 105 s-1, ΦPL: 90%), which contains a D-A moiety that itself is not TADF. The sensitizer-free OLEDs with DtCzBN-CNBT2 achieve a record-high maximum external quantum efficiency (EQEmax) of 40.2% and showed milder efficiency roll-off (EQE1000 of 20.7%) compared to the DtCzBN-CNBT1-based devices (EQEmax of 37.1% and EQE1000 of 11.9%).

Cascade Effect of a Dimerized Thermally Activated Delayed Fluorescence Dendrimer

Thermally activated delayed fluorescence (TADF) emitters with a high horizontal orientation are highly essential for improving the external quantum efficiency (EQE) of organic light-emitting diodes; however, pivotal molecular design strategies to improve the horizontal orientation of solution-processable TADF emitters are still scarce and challenging. Herein, a phenyl bridge is adopted to connect the double TADF units, and generate a dimerized TADF dendrimer, D4CzBNPh-SF. Compared to its counterpart with a single TADF unit, the proof-of-the-concept molecule not only exhibits an improved horizontal dipole ratio (78 %) due to the π-delocalization-induced extended molecular conjugation, but also displays a faster reversed intersystem crossing rate constant (6.08×106 s-1) and a high photoluminescence quantum yield of 95 % in neat film. Consequently, the non-doped solution-processed device with D4CzBNPh-SF as the emitter achieves an ultra-high maximum EQE of 32.6 %, which remains at 26.6 % under a luminance of 1000 cd/m2. Furthermore, when using D4CzBNPh-SF as a sensitizer, the TADF-sensitized fluorescence device exhibits a high maximum EQE of 30.7 % at a luminance of 575 cd/m2 and a full width at half maximum of 36 nm.

An Azaryl-Ketone-Based Thermally Activated Delayed Fluorophore with Aggregation-Induced Emission for Efficient Organic Light-Emitting Diodes with Slow Efficiency Roll-Offs

Achieving the concurrent manifestation of thermally activated delayed fluorescence (TADF) and aggregation-induced emission (AIE) within a single molecular system is highly sought after for organic light-emitting diodes (OLEDs), yet remains rare. In this study, we present a novel TADF-AIE dye, named PQMO-PXZ, which has been designed, synthesized, and systematically characterized. Our comprehensive investigation, which includes structural analysis, theoretical calculations, and optical studies, evaluates the potential of PQMO-PXZ for integration into OLEDs. Unlike existing azaryl-ketone-based emitters, PQMO-PXZ exhibits red-shifted emission and enhanced luminescence efficiency, due to its rigid structure and strong intramolecular charge transfer characteristics. Significantly, PQMO-PXZ demonstrates pronounced AIE properties and TADF with a short delayed lifetime. When utilized as the emissive core, OLED devices based on PQMO-PXZ achieve a respectable external quantum efficiency of up to 11.8 % with minimal efficiency roll-off, underscoring PQMO-PXZ's promise as a highly efficient candidate for OLED applications.

A perspective on next-generation hyperfluorescent organic light-emitting diodes

Hyperfluorescence, also known as thermally activated delayed fluorescence (TADF) sensitized fluorescence, is known as a next-generation efficient and innovative process for high-performance organic light-emitting diodes (OLEDs). High external quantum efficiency (EQE) and good color purity are crucial parameters for display applications. Hyperfluorescent OLEDs (HF-OLEDs) take the lead in this respect as they utilize the advantages of both TADF emitters and fluorescent dopants, realizing high EQE with color saturation and long-term stability. Hyperfluorescence is mediated through Förster resonance energy transfer (FRET) from a TADF sensitizer to the final fluorescent emitter. However, competing loss mechanisms such as Dexter energy transfer (DET) of triplet excitons and direct charge trapping on the final emitter need to be mitigated in order to achieve fluorescence emission with high efficiency. Despite tremendous progress, appropriate guidelines and fine optimization are still required to address these loss channels and to improve the device operational lifetime. This perspective aims to provide an overview of the evolution of HF-OLEDs by reviewing both molecular and device design pathways for highly efficient narrowband devices covering all colors of the visible spectrum. Existing challenges and potential solutions, such as molecules with peripheral inert substitution, multi-resonant (MR) TADF emitters as final dopants, and exciplex-sensitized HF-OLEDs, are discussed. Furthermore, the operational device lifetime is reviewed in detail before concluding with suggestions for future device development.

Modulatory spin-flip of triplet excitons via diversiform electron-donating units for MR-TADF emitters towards solution-processed narrowband OLEDs

Multiple resonance thermally activated delayed fluorescence (MR-TADF) molecules are emerging as promising candidates for high-resolution organic light-emitting diode (OLED) displays, but MR-TADF emitters always suffer from an unsatisfactory rate constant of reverse intersystem crossing (k RISC) due to inherently low spin orbital coupling strength between excited singlet and triplet states. Herein, we systematically investigate the long-range charge transfer (LRCT) and heavy-atom effects on modulating the excited state natures and energy levels via integrating diversiform electron-donating units with the MR skeleton. Compared with unsubstituted analogues, newly designed MR-TADF emitters exhibit significantly boosted k RISC values and close-to-unity photoluminescence quantum yield especially for tBuCzBN-PXZ (2.5 × 105 s-1) and tBuCzBN-Ph-PSeZ (2.1 × 105 s-1). Leveraging these exceptional properties, the maximum external quantum efficiency values of tBuCzBN-PXZ- and tBuCzBN-Ph-PSeZ-based solution-processed OLEDs can reach 21.3% and 19.4%, which are in the first tier of reported solution-processed MR-TADF binary OLEDs without employing additional sensitizers. This study provides a framework for modulating photoelectrical properties of MR-TADF emitters through fastidiously regulating LRCT and heavy-atom effects.

High-performance deep-blue electroluminescence from multi-resonance TADF emitters with a spirofluorene-fused double boron framework

The development of multi-resonance thermally activated delayed fluorescence (MR-TADF) materials in the deep-blue region is highly desirable. A usual approach involves constructing an extended MR-TADF framework; however, it may also intensify aggregate-caused quenching issues and thereby reduce device efficiency. In this study, we develop a molecular design strategy that fuses the MR-TADF skeleton with 9,9'-spirobifluorene (SF) units to create advanced deep-blue emitters. The SF moiety facilitates high-yield one-shot bora-Friedel-Crafts reaction towards an extended skeleton and mitigates interchromophore interactions as a steric group. Our findings reveal that orbital interactions at the fusion site significantly influence the electronic structure, and optimizing the fusion mode allows for the development of emitters with extended conjugation length while maintaining non-bonding character. The proof-of-concept emitter exhibits narrowband emission in the deep-blue region, a near-unity photoluminescence quantum yield, and a fast k RISC of 2.4 × 105 s-1. These exceptional properties enable the corresponding sensitizer-free OLED to achieve a maximum external quantum efficiency (EQEmax) of 39.0% and Commission Internationale de l'Eclairage (CIE) coordinates of (0.13, 0.09). Furthermore, the hyperfluorescence device realizes an EQEmax of 40.4% with very low efficiency roll-off.

Spirobifluorene-fused strategy enables pure-green multiple resonance emitters with low efficiency roll-off

Herein, we present a molecular design strategy centered on the spiroannulation of the MR-core skeleton to fabricate green MR-emitters and reduce device efficiency roll-off. Fusing 9,9'-spirobifluorene into the central framework of MR-emitters facilitates the distribution of the highest occupied molecular orbital (HOMO) across the spiro units, leading to a red-shifted emission and giving rise to a pure-green MR-emitter (DPhCz-SFBN) with the Commission Internationale de l'Eclairage (CIE) coordinates of [0.16, 0.74] in toluene solution, closely matching the BT.2020 standard for green. Additionally, the resultant highly twisted hetero[6]helicene conformation and a nearly perpendicular conformation of spirocycle structure effectively minimize close π-π stacking interactions among the MR-emitting cores, thereby reducing exciton quenching. Consequently, organic light-emitting diodes (OLEDs) based on DPhCz-SFBN exhibit a high maximum quantum efficiency (EQEmax) of 32.8% with low efficiency roll-off, maintaining an EQE of 23.2% at a practical luminance level of 5000 cd m-2.

A theoretical investigation for improving the performance of non-fullerene organic solar cells through side-chain engineering of BTR non-fused-ring electron acceptors

In the current quantum chemical study, indacenodithiophene donor core-based the end-capped alterations of the reference chromophore BTR drafted eight A2-A1-D-A1-A2 type small non-fullerene acceptors. All the computational simulations were executed under MPW1PW91/6-31G (d, p) level of DFT. The UV-Vis absorption, open circuit voltage, electron affinity, ionization potential, the density of states, reorganization energy, orbital analysis, and non-covalent interactions were studied and compared with BTR. Several molecules of our modeled series BT1-BT8 have shown distinctive features that are better than those of the BTR. The open circuit voltage (VOC) of BT5 has a favorable impact, allowing it to replace BTR in the field of organic solar cells. The charge carrier motilities for proposed molecules generated extraordinary findings when matched to the reference one (BTR). Further charge transmission was confirmed by creating the complex with a PM6 donor molecule. The remarkable dipole moment contributes to the formation of non-covalent bond interactions with chloroform, resulting in superior charge mobility. Based on these findings, it can be said that every tailored molecule has the potential to surpass chromophore molecule (BTR) in OSCs. So, all tailored molecules may enhance the efficiency of photovoltaic cells due to the involvement of potent terminal electron-capturing acceptor2 moieties. Considering these obtained results, these newly presented molecules can be regarded for developing efficient solar devices in the future.

Dual Sulfone-Bridged Triphenylamine Heteroaromatics for High-Performance Blue Organic Electroluminescence

Polycyclic heteroaromatics (PHAs) are a highly versatile class of functional materials, especially applicable as efficient luminophores in organic light-emitting diodes (OLEDs). Those constructed by tethered phenyl surrounding the main group center attract extensive attention due to their excellent OLED device performance. However, the development of such a class of emitters is often limited to boron, nitrogen-doped π-conjugated heterocycles. Herein, we proposed a novel kind of blue emitter by constructing a donor-acceptor molecular configuration, utilizing a dual sulfone-bridged triphenylamine (BTPO) core and mono/di-diphenylamine (DPA) substituents. The twisted D-A molecular structures and appropriate donor strength facilitate the effective separation of natural transition orbitals, endowing the emitters with charge-transfer dominant hybridized local and charge-transfer characteristics for the excited states. Both BTPO-DPA and BTPO-2DPA own small S1-T1 splitting energy, thus demonstrating blue thermally activated delayed fluorescence. The more symmetrical structure and enhanced CT features brought by additional DPA moiety confer BTPO-2DPA with a shorter delayed fluorescence lifetime, a higher fluorescence quantum yield and narrower emission. Therefore, BTPO-2DPA based OLED devices exhibit superior blue electroluminescence performance, with external quantum efficiencies reaching 12.31 %.

10-Dibenzothiophenyl-9,9-diphenylacridane-based multiple resonance emitters for high-efficiency narrowband green OLEDs with CIE y > 0.7 at high doping concentrations

Multiple resonance emitters are attractive for high-color-purity organic light-emitting diodes (OLEDs) because of their unique narrowband emissions; however, they are typically used at low doping concentrations (≤15 wt%) due to aggregation-caused quenching and spectral broadening induced by planar molecular skeletons. Here, we report two multiple resonance emitters (BThPAc-1 and BThPAc-2) consisting of a 10-dibenzothiophenyl-9,9-diphenylacridane segment for efficient narrowband green emission at high doping concentrations. The dibenzothiophenyl-9,9-diphenylacridane segment contains two carbon-bridged phenyl rings as steric groups to inhibit intermolecular aggregation and a dibenzothiophene unit to extend conjugation and red-shift the emission to the green region. The resultant emitters exhibit narrowband emissions that peaked at 509-510 nm with a full width at half-maximum (FWHM) of 32 nm in 1 wt% doping films, which are maintained at less than 35 nm even in neat films. Remarkably, OLEDs employing the emitters reveal pure-green electroluminescence with a maximum external quantum efficiency of 20.3% and CIE coordinates of (0.18, 0.72) at 30 wt% doping concentration, which represents the best color coordinates for green multiple resonance OLEDs at high doping concentrations.

Intramolecular exciplex featuring a bis-sp3 C-locked acceptor-donor-acceptor sandwich

Intramolecular exciplex systems featuring thermally activated delayed fluorescence (TADF) have garnered significant attention in the realm of organic light-emitting diodes (OLEDs). Nonetheless, the occurrence of organic sandwich intramolecular exciplexes remains rare due to structural limitations and synthetic challenges. Herein, we present a novel rigid acceptor-donor-acceptor (A-D-A) sandwich complex, dSFQP, characterized by two sp3 C-locking moieties. This compound exhibits TADF characteristics facilitated by a multiple through-space charge-transfer process. X-ray crystallographic analysis confirms the distinctive sandwich configuration. The parallel spatial arrangement and minimized A-D-A configuration enhance electronic interactions, resulting in a high photoluminescence quantum yield, rapid reverse intersystem crossing rate, and sluggish nonradiative decay rate. OLEDs employing dSFQP as the dopant achieve a maximum external quantum efficiency (EQE) of 28.5% with a low efficiency roll-off of merely 2.8% at 1000 cd m-2. Even at a high brightness of 10 000 cd m-2, the EQE remains notably high at 17.5%. Our current results provide an effective way to further innovate the design of new organic charge-transfer complexes.

Structurally Tunable Donor-Bridge-Fluorophore Architecture Enables Highly Efficient and Concentration-Independent Narrowband Electroluminescence

Luminescent materials with narrowband emission have extraordinary significance for developing ultrahigh-definition display. B-N-containing multiple resonance thermally activated delayed fluorescence (MR-TADF) materials are strong contenders. However, their device performances pervasively encounter detrimental aggregation-caused quenching effect that is highly vulnerable to doping concentration, complicating device fabrication. Therefore, constructing highly efficient and concentration-independent MR-TADF emitters is of pragmatic importance for improving device controllability and reproducibility, simplifying manufacturing procedures, and conserving production costs. Here, by systematic arrangement of donor triphenylamine and fluorophore BNCz on distinct bridges, a spatial confinement strategy has been developed with a donor-bridge-fluorophore architecture. Structurally fine modulation and progressive evolution to construct molecular entities with congested steric hindrance effect that can suppress intermolecular interactions without substantially affecting the luminescence tone of fluorophore BNCz, resulting in highly efficient and concentration-independent narrowband emitters; through isomer engineering, two isomers BN-PCz-TPA and TPA-PCz-BN with different crystal stacking patterns are synthesized by altering the connection mode between triphenylamine and BNCz. As a result, BN-PCz-TPA-based device showcases maximum external quantum efficiency (EQE) of 36.3% with narrow full-width at half-maximum of 27 nm at 10 wt% doping concentration. Even at 20 wt% doping concentration, the maximum EQE remains at 32.5% and the emission spectrum is almost unchanged.

Expanding Multiple-Resonance Structure of a Double-Borylated Skeleton by Fusing with Indolocarbazole a Multiple-Resonance Donor for Narrowband Green Emission

Double-borylated multiple-resonance (MR) skeletons are promising templates for high performance, while the chemical design space is relatively limited. Peripheral segments are often used to decorate/fuse MR skeletons and modulate the photophysics but they can also cause unwanted spectral broadening. Herein, a narrowband MR emitter ICzDBA by fusing an MR-featured donor segment indolocarbazole into a double-borylated MR skeleton is developed. In ICzDBA, the nitrogen atom located away from the core benzene ring can also contribute to the generation of the overall MR-featured distribution through the long-range conjugation effect, along with the other boron/nitrogen atoms on the phenyl center. Thus, ICzDBA in toluene displays a narrowband emission peaking at 507 nm with a full width at half maximum of merely 20 nm (0.09 eV). Moreover, organic light-emitting diode devices using ICzDBA emitter exhibit ultrapure green emission with Commission Internationale de l'Eclairage (CIE) coordinates of (0.27, 0.70) and a high external quantum efficiency of 32.5%. These results manifest the importance of MR characters of peripheral decorations/fusions in preserving the narrowband features of MR skeletons, which provides a solution for further expanding MR structures with well-maintained narrowband characters.

Elevating the upconversion performance of a multiple resonance thermally activated delayed fluorescence emitter via an embedded azepine approach

Multiple resonance thermally activated delayed fluorescence (MR-TADF) emitters hold promise for efficient organic light-emitting diodes (OLEDs) and wide gamut displays. An azepine donor is introduced into the boron-nitrogen system for the first time. The highly twisted conformation of a seven-ring embedded new molecule, TAzBN, increases the intermolecular distances, suppressing self-aggregation emission quenching. Meanwhile, the azepine donor is crucial to achieve a narrow singlet-triplet gap (0.03 eV) as well as boost the reverse intersystem crossing (RISC) rate to 8.50 × 105 s-1. It is noteworthy that TAzBN demonstrates an impressive photoluminescence quantum yield of 94%. In addition, its nonsensitized OLED displayed a remarkable external quantum efficiency (EQEmax) with values peaking at 27.3%, and an EQE of 21.4% at 500 cd m-2. This finding shows that when TAzBN is used at a high concentration of 10 wt%, its device maintains efficiency even at higher brightness levels, highlighting TAzBN's resistance to aggregation quenching. Furthermore, TAzBN enantiomers showed circularly polarized photoluminescence characteristics with dissymmetry factors |g PL| of up to 1.07 × 10-3 in doped films. The curved heptagonal geometry opens an avenue to design the MR-TADF emitters with fast spin-flip and chiroptical properties.

Stepwise Toward Pure Blue Organic Light-Emitting Diodes by Synergetically Locking and Shielding Carbonyl/Nitrogen-Based MR-TADF Emitters

Deep-blue multi-resonance (MR) emitters with stable and narrow full-width-at-half-maximum (FWHM) are of great importance for widening the color gamut of organic light-emitting diodes (OLEDs). However, most planar MR emitters are vulnerable to intermolecular interactions from both the host and guest, causing spectral broadening and exciton quenching in thin films. Their emission in the solid state is environmentally sensitive, and the color purity is often inferior to that in solutions. Herein, a molecular design strategy is presented that simultaneously narrows the FWHM and suppresses intermolecular interactions by combining intramolecular locking and peripheral shielding within a carbonyl/nitrogen-based MR core. Intramolecularly locking carbonyl/nitrogen-based bears narrower emission of 2,10-dimethyl-12,12-diphenyl-4H-benzo[9,1]quinolizino[3,4,5,6,7-defg]acridine-4,8(12H)-dione in solution and further with peripheral-shielding groups, deep-blue emitter (12,12-diphenyl-2,10-bis(9-phenyl-9H-fluoren-9-yl)-4H-benzo[9,1]quinolizino[3,4,5,6,7-defg]acridine-4,8(12H)-dione, DPQAO-F) exhibits ultra-pure emission with narrow FWHM (c.a., 24 nm) with minimal variations (∆FWHM ≤ 3 nm) from solution to thin films over a wide doping range. An OLED based on DPQAO-F presents a maximum external quantum efficiency (EQEmax) of 19.9% and color index of (0.134, 0.118). Furthermore, the hyper-device of DPQAO-F exhibits a record-high EQEmax of 32.7% in the deep-blue region, representing the first example of carbonyl/nitrogen-based OLED that can concurrently achieve narrow bandwidth in the deep-blue region and a high electroluminescent efficiency surpassing 30%.

Stepwise Charge/Energy Transfer in MR-TADF Molecule-Doped Exciplex for Ultralong Persistent Luminescence Activated with Visible Light

Organic long-persistent luminescence (OLPL), which relies on energy storage for delayed light emission by the charge separation state, has attracted intense attention in various optical applications. However, charge separation (CS) is efficient only under ultraviolet excitation in most OLPL systems because it requires a driving force from the large energy difference between the local excited (LE) and charge transfer (CT) states. In this study, a multiresonance thermally activated delayed fluorescence (MR-TADF) molecule is incorporated into an exciplex system to achieve efficient OLPL in a composite material activated by visible light via a stepwise charge/energy transfer process. The enhanced absorption of the composite material facilitated a tenfold increase in the duration of the OLPL, which can last for several hours under visible light excitation. The excited state of the MR-TADF molecule tends to charge transfer to the acceptor, followed by energy transfer to the exciplex, which benefits from the small difference between the LE and CT states owing to the inherent CS characteristics of the opposing resonance effect. Afterglow displays of these composite materials are fabricated to demonstrate their considerable potential in encryption patterns and emergency lights, which take advantage of their excellent processability, visible light activation, and tunable luminescence properties.

Efficient Deep-Blue Multiple-Resonance Emitters Based on Azepine-Decorated ν-DABNA for CIEy below 0.06

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.

A diphenylphosphine oxide decorated multi-resonance TADF emitter for narrowband green electroluminescence with an EQE of 32.4

A new narrowband thermally activated delayed fluorescence emitter, PhCzBN-PO, was developed by incorporating the diphenylphosphine oxide (DPPO) group into a multi-resonance core. The unique properties of DPPO enabled PhCzBN-PO to achieve pure green emission and a nonplanar structure. The resulting electroluminescent devices achieved high external quantum efficiencies up to 32.4% with extremely low efficiency roll-off and pure-green emission with Commission Internationale de L'Eclairage (CIE) coordinates of (0.24, 0.67).

Synthetic progress of organic thermally activated delayed fluorescence emitters via C-H activation and functionalization

Thermally activated delayed fluorescence (TADF) emitters have become increasingly prominent due to their promising applications across various fields, prompting a continuous demand for developing reliable synthetic methods to access them. This review aims to highlight the progress made in the last decade in synthesizing organic TADF compounds through C-H bond activation and functionalization. The review begins with a brief introduction to the basic features and design principles of TADF emitters. It then provides an overview of the advantages and concise development of C-H bond transformations in constructing TADF emitters. Subsequently, it summarizes both transition-metal-catalyzed and non-transition-metal-promoted C-H bond transformations used for the synthesis of TADF emitters. Finally, the review gives an outlook on further challenges and potential directions in this field.

B‒N covalent bond-involved π-extension of multiple resonance emitters enables high-performance narrowband electroluminescence

Multi-boron-embedded multiple resonance thermally activated delayed fluorescence (MR-TADF) emitters show promise for achieving both high color-purity emission and high exciton utilization efficiency. However, their development is often impeded by a limited synthetic scope and excessive molecular weights, which challenge material acquisition and organic light-emitting diode (OLED) fabrication by vacuum deposition. Herein, we put forward a B‒N covalent bond-involved π-extension strategy via post-functionalization of MR frameworks, leading to the generation of high-order B/N-based motifs. The structurally and electronically extended π-system not only enhances molecular rigidity to narrow emission linewidth but also promotes reverse intersystem crossing to mitigate efficiency roll-off. As illustrated examples, ultra-narrowband sky-blue emitters (full-width at half-maximum as small as 8 nm in n-hexane) have been developed with multi-dimensional improvement in photophysical properties compared to their precursor emitters, which enables narrowband OLEDs with external quantum efficiencies (EQEmax) of up to 42.6%, in company with alleviated efficiency decline at high brightness, representing the best efficiency reported for single-host OLEDs. The success of these emitters highlights the effectiveness of our molecular design strategy for advanced MR-TADF emitters and confirms their extensive potential in high-performance optoelectronic devices.

Thermally Activated Delayed Fluorescence with Nanosecond Emission Lifetimes and Minor Concentration Quenching: Achieving High-Performance Nondoped and Doped Blue OLEDs

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.

Understanding the bio-crystallization: An insight to therapeutic relevance

In the realm of biomedical engineering and materials science, the synthesis of biomaterials plays a pivotal role in advancing therapeutic strategies for regeneration of tissues. The deliberate control of crystallization processes in biomaterial synthesis has emerged as a key avenue for tailoring the properties of these materials, enabling the design of innovative solutions for a wide array of medical applications. This review delves into the interplay between controlled crystallization and biomaterial synthesis, exploring its multifaceted applications in the therapeutic domains. The investigation encompasses a wide spectrum of matrices, ranging from small molecules to large biomolecules, highlighting their unique contributions in modulating crystallization processes. Furthermore, the review critically assesses the analytical techniques and methodologies employed to probe and characterize the depths of crystallization dynamics. Advanced imaging, spectroscopic, and computational tools are discussed in the context of unraveling the intricate mechanisms governing nucleation and crystallization processes within the organic matrix. Finally we delve in the applications of such advance material in therapeutics of hard and soft tissues.

Reverse intersystem crossing mechanisms in doped triangulenes

Thermally activated delayed fluorescence (TADF) has emerged as one of the most promising strategies in the quest for organic light emitting diodes with optimal performance. This computational study dissects the mechanistic intricacies of the central photophysical step, reverse intersystem crossing (rISC) in N and B doped triangulenes as potential multi-resonance TADF compounds. Optimal molecular patterns conducive to efficient rISC, encompassing dopant atom size, number, and distribution, are identified. Additionally, we assess various electronic structure methods for characterizing TADF-relevant molecular systems. The findings identify the distinct role of the direct and mediated mechanisms in rISC, and provide insights into the design of advanced TADF chromophores for next-generation OLED technology.

Synergetic Modulation of Steric Hindrance and Excited State for Anti-Quenching and Fast Spin-Flip Multi-Resonance Thermally Activated Delayed Fluorophore

Multi-resonance thermally activated delayed fluorescence (MR-TADF) materials hold great promise for advanced high-resolution organic light-emitting diode (OLED) displays. However, persistent challenges, such as severe aggregation-caused quenching (ACQ) and slow spin-flip, hinder their optimal performance. We propose a synergetic steric-hindrance and excited-state modulation strategy for MR-TADF emitters, which is demonstrated by two blue MR-TADF emitters, IDAD-BNCz and TIDAD-BNCz, bearing sterically demanding 8,8-diphenyl-8H-indolo[3,2,1-de]acridine (IDAD) and 3,6-di-tert-butyl-8,8-diphenyl-8H-indolo[3,2,1-de]acridine (TIDAD), respectively. These rigid and bulky IDAD/TIDAD moieties, with appropriate electron-donating capabilities, not only effectively mitigate ACQ, ensuring efficient luminescence across a broad range of dopant concentrations, but also induce high-lying charge-transfer excited states that facilitate triplet-to-singlet spin-flip without causing undesired emission redshift or spectral broadening. Consequently, implementation of a high doping level of IDAD-BNCz resulted in highly efficient narrowband electroluminescence, featuring a remarkable full-width at half-maximum of 34 nm and record-setting external quantum efficiencies of 34.3 % and 31.8 % at maximum and 100 cd m-2, respectively. The combined steric and electronic effects arising from the steric-hindered donor introduction offer a compelling molecular design strategy to overcome critical challenges in MR-TADF emitters.

Combined DFT and QM/MM Modeling on Multifunctional TADF Sensitizers and Hot-Exciton Emitters via Carborane Triads for Blue Hyperfluorescent OLEDs

The scarcity of novel luminogens significantly impedes the advancement of TADF sensitizers and hot exciton emitters, attracting considerable attention for their potential to enhance energy conversion efficiencies in hyperfluorescent OLEDs. In this study, a systematic investigation is employed to design and develop multifunctional materials based on carborane cores through DFT and TD-DFT methods. In pursuit of this objective, 45 carborane triad-type molecules were systematically designed using four donors and two acceptor units. Electronic structure calculations revealed that (i) the singlet, triplet, ΔEST, and SOC values exhibit an increased trend as the carborane core shifts from ortho to meta to para, while an increase in donor strength on the core leads to a decrease in these values. (ii) Moreover, there is a decrease in reorganization energies, absorption wavelengths, ISC, and RISC rates as the carborane switches from ortho to meta to para while witnessing an increase in donor strength. The QM/MM study reveals that para carborane's restricted intramolecular motions improve its solid-state aggregation over ortho carborane and solution phases. Interestingly, carborane triads featuring P-DMB and P-BODIPY acceptor units satisfy the desired criteria for multifunctional TADF sensitizers and hot exciton emitters, respectively.

Precision-Engineered Medium-Sized Molecular Host and Emitter for Ensuring Consistent Performance in Solution-Processed Narrowband OLEDs

In this study, two novel multiple resonance (MR) emitters, DtCzBN and Cy-DtCzBN, were designed based on the well-known BCzBN structure and synthesized for narrowband solution-processed organic light-emitting diodes (OLEDs). Cy-DtCzBN possesses a dimeric V-shaped structure formed by coupling two individual DtCzBN units via a nonconjugated cyclohexane linker. When compared with DtCzBN, Cy-DtCzBN, as a medium-sized molecule, was found to maintain the optical and photophysical properties of the corresponding monomeric unit, DtCzBN, but exhibits high thermal stability, excellent solubility, and good film-forming ability. Additionally, solution-processed OLEDs were fabricated by using two sets of molecules: one set of small molecular hosts and emitters (i.e., mCP and DtCzBN) and the other set of medium-sized molecular hosts and emitters (i.e., Cy-mCP and Cy-DtCzBN). Notably, devices using medium-sized molecular hosts and emitters exhibited similar optical and photophysical properties but showed significantly improved reproducibility and thermal stability compared with those based on small molecular hosts and emitters. Our current study provides some insights into molecular design strategies for thermally stable hosts and emitters, which are highly suitable for solution-processed OLEDs.

Highly efficient multi-resonance thermally activated delayed fluorescence material toward a BT.2020 deep-blue emitter

An ultrapure deep-blue multi-resonance-induced thermally activated delayed fluorescence material (DOB2-DABNA-A) is designed and synthesized. Benefiting from a fully resonating extended helical π-conjugated system, this compound has a small ΔEST value of 3.6 meV and sufficient spin-orbit coupling to exhibit a high-rate constant for reverse intersystem crossing (kRISC = 1.1 × 106 s-1). Furthermore, an organic light-emitting diode employing DOB2-DABNA-A as an emitter is fabricated; it exhibits ultrapure deep-blue emission at 452 nm with a small full width at half maximum of 24 nm, corresponding to Commission Internationale de l'Éclairage (CIE) coordinates of (0.145, 0.049). The high kRISC value reduces the efficiency roll-off, resulting in a high external quantum efficiency (EQE) of 21.6% at 1000 cd m-2.

Suppression of Dexter transfer by covalent encapsulation for efficient matrix-free narrowband deep blue hyperfluorescent OLEDs

Hyperfluorescence shows great promise for the next generation of commercially feasible blue organic light-emitting diodes, for which eliminating the Dexter transfer to terminal emitter triplet states is key to efficiency and stability. Current devices rely on high-gap matrices to prevent Dexter transfer, which unfortunately leads to overly complex devices from a fabrication standpoint. Here we introduce a molecular design where ultranarrowband blue emitters are covalently encapsulated by insulating alkylene straps. Organic light-emitting diodes with simple emissive layers consisting of pristine thermally activated delayed fluorescence hosts doped with encapsulated terminal emitters exhibit negligible external quantum efficiency drops compared with non-doped devices, enabling a maximum external quantum efficiency of 21.5%. To explain the high efficiency in the absence of high-gap matrices, we turn to transient absorption spectroscopy. It is directly observed that Dexter transfer from a pristine thermally activated delayed fluorescence sensitizer host can be substantially reduced by an encapsulated terminal emitter, opening the door to highly efficient 'matrix-free' blue hyperfluorescence.

Organic Optoelectronic Materials: A Rising Star of Bioimaging and Phototherapy

Recently, many organic optoelectronic materials (OOMs), especially those used in organic light-emitting diodes (OLEDs), organic solar cells (OSCs), and organic field-effect transistors (OFETs), are explored for biomedical applications including imaging and photoexcited therapies. In this review, recently developed OOMs for fluorescence imaging, photoacoustic imaging, photothermal therapy, and photodynamic therapy, are summarized. Relationships between their molecular structures, nanoaggregation structures, photophysical mechanisms, and properties for various biomedical applications are discussed. Mainly four kinds of OOMs are covered: thermally activated delayed fluorescence materials in OLEDs, conjugated small molecules and polymers in OSCs, and charge-transfer complexes in OFETs. Based on the OOMs unique optical properties, including excitation light wavelength and exciton dynamics, they are respectively exploited for suitable biomedical applications. This review is intended to serve as a bridge between researchers in the area of organic optoelectronic devices and those in the area of biomedical applications. Moreover, it provides guidance for selecting or modifying OOMs for high-performance biomedical uses. Current challenges and future perspectives of OOMs are also discussed with the hope of inspiring further development of OOMs for efficient biomedical applications.