International Commission On Illumination Research Articles

N-Alkyl Chain Induced Molecular Aggregation in Mononuclear Gold(I)-N-Heterocyclic Carbene Complexes for Blue Light Emitting Applications.

The gold(I) N-heterocyclic carbene (NHC) molecule exhibits outstanding luminescent properties along with high thermal stability due to its strong carbene gold bond. Gold(I)-NHC complexes are known to emit green to yellow color, while blue emission is limited. Herewith, we report the photoluminescence and thermal stability correlation between blue emitting mononuclear gold(I)-NHC chloride complexes, N-(9-anthracenyl)-N'(n-alkyl)imidazol-2-ylidene gold(I) chloride (alkyl=n-butyl (1), n-pentyl (2), n-hexyl (3)). These complexes were synthesized by transmetallation route and characterized by FT-IR, NMR, TGA, and single crystal X-ray diffraction analysis. The solid-state study reveals a unique molecular packing due to hydrogen bonding, aurophilic interaction, and CH⋅⋅⋅π interactions in all 1-3. In addition, the π⋅⋅⋅π stacking has been found in 1. All these complexes show good thermal stability due to the strong metal-ligand bond strength along with crystal packing. In addition, 1-3 emits a blue colour in both solution and crystalline state. The quantum yield in the crystalline state was found to be higher for 1 (22.44 %) compared to 2 (9.90 %), and 3 (14.98 %). A similar high quantum yield for blue-emitting gold(I)-NHC chloride complex is rare. This promising quantum yield for 1 can be ascribed to the crystal packing effect. The theoretical calculations were carried out to understand the electronic and structural properties of 1-3. Computational studies revealed the origin of the luminescence behaviour of complexes. The blue light emitting thin film and LED are demonstrated using 1 exhibited the emission peak at the blue region with Commission Internationale de L'Eclairage (CIE) coordinates near the National Television Standards Committee (NTSC) value.

Olivine-type germanate phosphors doped with Ln3+ (Ln = Eu, Dy) for solid-state lighting

Olivine-type germanate ceramics doped with Ln3+ ions (where Ln = Eu, Dy) as potential candidates to generate visible luminescence were studied. Analysis of microstructure and phase identification in systems obtained using the solid-state reaction method indicate that ceramics Li2ZnGeO4 and Li2MgGeO4 crystallize in a monoclinic crystal lattice, and samples consist of agglomerates that differ in size and shape. The spectroscopic properties of the ceramics align with the structure, and crucial parameters like the R/O or Y/B ratio and luminescence lifetime strongly depend on the type of ceramic samples. The luminescence spectra for germanate ceramics were recorded depending on the excitation wavelength and analyzed in detail. The Commission Internationale de l’Éclairage (CIE) chromaticity coordinates (x, y) were calculated from the emission spectra. It was observed that the color parameters change when the excitation wavelength and composition are modified. Our results indicate that olivine-type germanate ceramics doped with Eu3+ and Dy3+ ions exhibit red-orange and yellow-white emissions, respectively.

A Tailored TADF Emitter Based on Diphenylacetylene Anthracene Derivatives for Highly Efficient Solution-Processed Pure Red Organic Light-Emitting Diodes.

It holds enormous significance for red thermally activated delayed fluorescence (TADF) emitters to develop organic light-emitting diodes (OLEDs) with high efficiency and high color purity, which remains challenging for highly efficient solution-processed red TADF emitters due to the limitation of severe nonradiative decays. Herein, a red TADF emitter containing space interactions, 4,4'-(9,10-bis(phenylethynyl)anthracene-1,8-diyl)bis(N,N-bis(4-methoxyphenyl)aniline) (DBP-2MOTPA), is designed and synthesized, composed of ethynyl as the acceptor and methoxytriarylamine (MOTPA) as the donor. The triphenylamine donor unit decorated with peripheral methoxy units not only improves the solubility for the solution-processed technology but also increases the electron-donating ability. The highly twisted donor-π-acceptor (D-π-A) architecture generates a small energy gap (ΔEST) of 0.14 eV, and the appropriate overlap of highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) leads to a supernal photoluminescence quantum yield (ΦPL) of 68%. Consequently, the nondoped device based on DBP-2MOTPA with Commission Internationale de l'Eclairage (CIE) at (0.67, 0.33) exhibits the pure red emission, which satisfies the Rec.1931 standard red gamut (0.67, 0.33) and approaches the Rec.2020 standard (0.71, 0.29). Moreover, the doped devices employing DBP-2MOTPA as the emitter exhibit a maximum external quantum efficiency (EQE) of 6.09%, which is among the effective values in the solution-processed red TADF-OLEDs.

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.

Development of highly thermal-stable blue emitting Y4Al2O9:Bi3+ phosphors for w-LEDs, fingerprint and data security applications

A new blue-emitting Y4Al2O9:Bi3+ (YAO:Bi3+) phosphor is synthesized using the solution combustion method with mushroom extract as a binder. Its structural properties, concentration effects, temperature-dependent luminescence, and performance in LED devices are thoroughly investigated. Upon excitation at 367 nm, a strong blue light emission at 423 nm is observed, attributed to the 3P1→1S0 transition of Bi3+. The quantum efficiency reached approximately 63.5 %. The CIE diagram shows that the emission colour falls within the intense blue region, achieving a colour purity (CP) of 94 %. YAO:Bi3+ exhibits strong absorption in the near-ultraviolet range (330–400 nm), making it suitable for LEDs powered by near-ultraviolet chips. A thermal quenching experiment revealed an activation energy (Ea) of 0.323 eV, indicating that this YAO:Bi3+ phosphor possesses good thermal stability. This study showcases the use of YAO:Bi3+ phosphor in encapsulated LED devices. The device’s Commission Internationale de l’Éclairage (CIE) coordinates are (0.325, 0.310), with a high colour rendering index (CRI) of 94.70 and a low correlated colour temperature (CCT) of 5915 K at a current of 120 mA. These properties indicate that this phosphor is suitable for developing white LED devices powered by near-ultraviolet chips. The optimized YAO:Bi3+ phosphor is employed to enhance the detection of Level I-III fingerprint (FP) details with high resolution and contrast, showing effective visualization of latent fingerprints (LFPs) on various substrates. Furthermore, it is used as a model for developing fluorescent ink, which is applied to different media. The results suggest that YAO:Bi3+ phosphor has significant potential for applications in w-LEDs, advanced forensics, and anti-counterfeiting ink technologies.

Unveiling the dual-state emissive behaviour of 4,6-diarylpyrimidin-2-amines through a plug-and-play approach

We present here a series of 4,6-diarylpyrimidin-2-amine derivatives (5a-j) with tunable optical properties both in the solid and solution states. Our plug-and-play fluorophore design demonstrates that the aryl groups at the 4th and 6th positions of the 2-aminopyrimidine core enable distinct optical characteristics for each derivative. The fluorophore design concept was validated using theoretical and spectroscopic methods. The designed compounds were synthesised in moderate to good yields, and their structures were confirmed via IR, NMR, HRMS, and single-crystal XRD analyses. Optical studies revealed that varying the aryl substituents significantly impacts absorption, emission, and bandgap values in both phases. The absolute quantum yields (ϕF) of the synthesised derivatives ranged from 8.11 to 71.00% in DMF and 5.86–29.43% in thin films, with fluorescence lifetimes (τ) between 0.8 and 1.5 ns in DMF and 0.63–3.16 ns in films, respectively. CIE (Commission Internationale de l’Éclairage) diagrams indicate blue-green emission for 5a-j in the visible spectrum. The electrochemical analysis confirmed that the HOMO/LUMO (Highest Occupied Molecular Orbital/Lowest Unoccupied Molecular Orbital) energy levels can be modulated by altering the substituent rings. These results highlight the dual-state emission properties of 2-aminopyrimidine fluorophores, demonstrating their potential for a wide range of optoelectronic and advanced applications.

Synthesis of thermally stable orange light-emitting phosphors: characterization and investigations of Sm3+-doped CsCaF3 phosphors for solid-state-lighting applications

In this study, we synthesized and characterized pure CsCaF3 and CsCaF3 doped with samarium (Sm3+) ions using a solid-state method. X-ray diffraction analysis was employed to examine the crystal structure, while field emission scanning electron microscopy analyzed the surface morphology of the doped sample. A color coordinate graph was used to calculate the color, with the Commission Internationale de l'Eclairage (CIE) fitting the color of both pure and doped samples. Upon excitation at 405 nm (6H5/2→6F7/2 transition), the doped CsCaF3 emitted an orange light. The CsCaF3:Sm3+ sample (0.8 mol%) displayed 86% color purity and a color temperature of 2191 K, making it suitable for lighting applications. The thermoluminescence (TL) curve of the beta-irradiated CsCaF3:Sm3+ (0.8 mol%) sample showed peaks at 174 °C and 297 °C. Preheating techniques eliminated the low-temperature peak, and the peak temperature of maximal TL intensity (Tm) was 297 °C. The activation energy (Ea) and frequency factor (s) were determined using the peak shape method and varying heating rates. The dosage response of CsCaF3:Sm3+ (0.8 mol%) was examined for potential dosimetry applications.

High-Performance Narrowband Pure-Green OLEDs with Gamut Approaching BT.2020 Standard: Deuteration Promotes Device Efficiency and Lifetime Simultaneously.

In order to fulfill the demand for ultrahigh definition organic light-emitting diodes (OLEDs), pure-green emitters with Commission Internationale de l'Éclairage (CIE) y-coordinate over 0.71 are in urgent demand. Meanwhile, the high device efficiency, small efficiency roll-off, and operational lifetime also remain challenging issues. In this work, a series of narrowband pure-green fluorescent emitters based on a double-boron (B) doped polycyclic aromatic hydrocarbons (PAHs) framework fused with naphthalene units is reported. The newly designed emitters realize green emission with peaks of 512-521nm and extremely narrow full-width at half-maxima (FWHMs) of 16-17nm in toluene solution. Utilizing these emitters in a phosphor-sensitized fluorescence (PSF) system, the resulting OLEDs exhibit pure green emission with peaks in the range of 514-526nm and very narrow FWHMs of 19-20nm. Notably, the devices based on the partially deuterated emitter, DBN-NaPh-d, not only achieve a maximum external quantum efficiency (EQEmax) as high as 35.2%, small efficiency roll-off, along with a CIEy of 0.74 but also showcase impressive operational stability with a long lifetime (LT50) of over 3000h at an initial luminance of 1000cdm-2. This work represents one of the highest device efficiencies and superior device stability among fluorescence emitter-based OLEDs.

Combustion Synthesis and Influence of Dy3+ ions on Structural and Photometric Attributes of Olivine-type LiMgPO4 Nanophosphors for Illumination Applications.

The low-cost technique of combustion synthesis was used to synthesize the trivalent Dysprosium (Dy3+) doped olivine type Lithium Magnesium Phosphate (LiMgPO4). X-ray diffraction (XRD) analysis verified the orthorhombic phase, corresponding to the space group Pnma. The crystallite size of 50.83nm was calculated using Debye-Scherre formula. FESEM technique was used to study the morphology of the sample which depicts its porous nature. High-Resolution Transmission Electron Microscopy (HRTEM) analysis provided an average particle size measurement of 65 ± 2.04nm. The phosphor's photoluminescence (PL) excitation spectrum revealed distinct peaks in the ultraviolet (UV) and near-ultraviolet (near UV) regions, aligning with the characteristics of Dy3+ ions. Four emission peaks were observed in the PL spectra at various wavelengths: 4F9/2→6H15/2 (482nm), 4F9/2→6H13/2 (578nm), 4F9/2→6H11/2 (663nm) and 4F9/2→6H9/2 (700nm). Near-white light emission was observed at the Commission International de l'Eclairage (CIE) coordinates of Dy3+ activated LiMgPO4 [LMP] phosphor, which were (x = 0.41, y = 0.42) with color purity of 49.20%. The band gap of the prepared phosphor was calculated using diffuse reflectance spectra, yielding a value of 4.47 ± 0.02eV. The results indicated that the synthesized phosphor had potential for various illumination applications when combined with other phosphors under near-UV stimulation.

Optical investigation of Dy3+/ Eu3+ co-activated K2NaAlF6 fluorophosphor for color tunable lighting system: Structural analysis and warm light generation

Nowadays, research is mostly focused on developing luminous materials. Specifically, compounds based on inorganic phosphorus have found widespread use in a variety of applications, like radiation dosimetry, field emission displays (FEDs), cathode ray tubes (CRTs), lamp industries, and white light emitting diodes (WLEDs). In order to achieve white light emission, we successfully synthesized single-host K2NaAlF6 co-doped with Dy3+/Eu3+ in this study utilizing the pechini sol-gel approach. Under UV light, the synthesized samples' luminescence characteristics were examined. XRD analysis verified K2NaAlF6's phase purity. The phosphor materials have a tendency to aggregate, as seen by SEM pictures. The K2NaAlF6:Dy3+ doped phosphors showed good excitation at 349 nm in photoluminescence (PL) experiments, with strong emission bands at 489 nm (blue) and 576 nm (yellow). Strong orange emissions were seen for K2NaAlF6: Eu3+ doped phosphors at 595 nm and 614 nm, which correspond to the 5D0→7F1 and 5D0→7F2 transitions in Eu3+ ions. When these rare earths were co-doped, intense red, yellow, and blue emissions were produced. The Commission Internationale de l'Eclairage (CIE) coordinates were used to calculate the colour characteristics of the luminous produced samples. Consequently, these results imply that Dy3+/Eu3+ co-doped K2NaAlF6 phosphors, when stimulated by UV LEDs, could be appropriate for creating reddish-orange and warm white lighting systems.

Efficient and Stable Narrowband Pure-Red Light-Emitting Diodes with Electroluminescence Efficiencies Exceeding 43.

Advanced multiresonance-induced thermally activated delayed fluorescence (MR-TADF) materials exhibit exceptional promise for applications in state-of-the-art organic light-emitting diodes (OLEDs) owing to their unique narrowband emissions and high luminescent efficiencies. Despite substantial progress with blue and green MR-TADF materials, the development of pure-red MR-TADF emitters has lagged behind, thereby hindering the advancement toward high-performance ultrahigh-definition OLED displays. Here, we propose an effective approach for designing pure-red MR-TADF molecules based on the integration of secondary electron-donating units and π-skeleton extension into MR cores, which enables not only a redshift of narrowband emission but also an acceleration of reverse intersystem crossing (RISC) rate. The proof-of-the-concept emitter BNTPA showcases a bright and saturated red emission centered at 613 nm with a full-width at half-maximum of 0.14 eV, together with a more than twofold increase in the RISC rate. As a result, TADF OLEDs based on BNTPA achieved a record maximum external quantum efficiency (EQEmax) of up to 35.2% with Commission Internationale de l'Eclairage (CIE) coordinates of (0.657, 0.343), approaching the coordinates of the National Television Standards Committee (NTSC) red standard. Moreover, phosphor-assisted fluorescence devices exploiting BNTPA as a terminal emitter exhibit an exceptional EQEmax of 43.3%, accompanied by improved operational stability.

Simple‐Structure and Anti‐Quenching Deep‐Blue Multi‐Resonance TADF Emitters Enable High‐Efficiency OLEDs with BT.2020 Blue Gamut

AbstractDeveloping highly efficient pure‐blue organic light‐emitting diodes (OLEDs) that meet the stringent BT.2020 standard by using multi‐resonance thermally activated delayed fluorescence (MR‐TADF) materials has long been a formidable challenge. In this study, a strategy is demonstrated for high‐performance blue MR‐TADF emitters by gradually decorating the MR framework with alkyl groups, and subsequently introducing a diarylamino group at the para‐position of boron atom. The proof‐of‐concept molecule, IPrBN‐mCP, exhibits a narrowband deep‐blue emission peaking at 452 nm, with a very narrow full‐width at half maximum (FWHM) of 19 nm in solution, and a remarkably high photoluminescence quantum yield (PLQY) approaching unity in doped films. As a result, OLEDs based on IPrBN‐mCP achieve not only a high maximum external quantum efficiency (EQEmax) of 33.4% but also ultrapure blue emission with a Commission Internationale de L'Eclairage (CIE) y value of 0.046, fully satisfying the BT.2020 blue standard. This represents the first OLED example fully meeting the rigorous color requirements of the BT.2020 blue standard while simultaneously achieving an EQE exceeding 30%.

Solution Processed Bilayer Metal Halide White Light Emitting Diodes.

Metal halide perovskites and perovskite-related organic metal halide hybrids (OMHHs) have recently emerged as a new class of luminescent materials for light emitting diodes (LEDs), owing to their unique and remarkable properties, including near-unity photoluminescence quantum efficiencies, highly tunable emission colors, and low temperature solution processing. While substantial progress has been made in developing monochromatic LEDs with electroluminescence across blue, green, red, and near-infrared regions, achieving highly efficient and stable white electroluminescence from a single LED remains a challenging and under-explored area. Here, a facile approach to generating white electroluminescence is reported by combining narrow sky-blue emission from metal halide perovskites and broadband orange/red emission from zero-dimensional (0D) OMHHs. For the proof of concept, utilizing TPPcarz+ passivated two-dimensional (2D) CsPbBr3 nanoplatelets (NPLs) as sky blue emitter and 0D TPPcarzSbBr4 as orange/red emitter (TPPcarz+ = triphenyl (9-phenyl-9H-carbazol-3-yl) phosphonium), white LEDs (WLEDs) with a solution processed bilayer structure have been fabricated to exhibit a peak external quantum efficiency (EQE) of 4.8% and luminance of 1507 cd m-2 at the Commission Internationale de L'Eclairage (CIE) coordinate of (0.32, 0.35). This work opens a new pathway for creating highly efficient and stable WLEDs using metal halide perovskites and related materials.

Spiro-Carbon-Locking and Sulfur-Embedding Strategy for Constructing Deep-Red Organic Electroluminescent Emitter with High Efficiency.

The discovery of multiple resonance thermally activated delayed fluorescence (MR-TADF) materials with remarkable narrowband emission has opened a new avenue for the development of organic light-emitting diodes (OLEDs) with high color purity. However, the lack of construction strategies for purely red MR-TADF materials significantly impedes their application in full-color high-definition displays. Herein, we propose a unique and handy approach of spiro-carbon-locking and sulfur-embedding strategy to modify the parent MR-TADF framework, resulting in a red MR-TADF emitter with high color purity. The reported MR-TADF molecule (namely, FSBN) demonstrates a pure red emission with an emission maximum of 621 nm in toluene solution. The OLED with FSBN as emitter exhibits Commission Internationale de l'Éclairage (CIE) coordinates of (0.67, 0.33), which exactly matches the red standard defined by the National Television Standards Committee (NTSC). Importantly, the single-host OLED achieves a high power efficiency (PE) of up to 50.1 lm W-1, suggesting the potential for the development of low power consumption red OLEDs.

Spiro‐Carbon‐Locking and Sulfur‐Embedding Strategy for Constructing Deep‐Red Organic Electroluminescent Emitter with High Efficiency

The discovery of multiple resonance thermally activated delayed fluorescence (MR‐TADF) materials with remarkable narrowband emission has opened a new avenue for the development of organic light‐emitting diodes (OLEDs) with high color purity. However, the lack of construction strategies for purely red MR‐TADF materials significantly impedes their application in full‐color high‐definition displays. Herein, we propose a unique and handy approach of spiro‐carbon‐locking and sulfur‐embedding strategy to modify the parent MR‐TADF framework, resulting in a red MR‐TADF emitter with high color purity. The reported MR‐TADF molecule (namely, FSBN) demonstrates a pure red emission with an emission maximum of 621 nm in toluene solution. The OLED with FSBN as emitter exhibits Commission Internationale de l’Éclairage (CIE) coordinates of (0.67, 0.33), which exactly matches the red standard defined by the National Television Standards Committee (NTSC). Importantly, the single‐host OLED achieves a high power efficiency (PE) of up to 50.1 lm W−1, suggesting the potential for the development of low power consumption red OLEDs.

Hybrid Local and Charge Transfer Emitters Utilizing Hyperconjugation Effect Towards Solution‐Processed Ultra‐Deep‐Blue OLEDs with External Quantum Efficiency Approaching 12 %

AbstractHybrid local and charge transfer (HLCT) excited state materials, which possess weak donor‐acceptor (D–A) pure organic structures, deserve one of the most promising efficient and stable blue emitters. Through high‐lying reverse intersystem crossing (hRISC) process, 75 % triplet excitons generated by electrical excitation could be harvested and utilized in organic light‐emitting diodes (OLEDs). However, there are still significant challenges to achieve high‐efficiency ultra‐deep‐blue HLCT emitters with low Commission Internationale de l'Eclairage (CIE) 1931 chromaticity coordinate y values. Here, a series of novel blue HLCT emitters based on spiro[1,8‐diazafluorene‐9,2′‐imidazole] structure were designed and synthesized by fine‐tuning the spiro[fluorene‐9,2′‐imidazole] core structure in our previous work through heteroatom substitution and hyperconjugation effect. The target emitters were endowed with excellent photophysical and electrochemical merits, thermal stability and solution processibility. The solution‐processed OLED based on 4′,5′‐bis(4‐(9H‐carbazol‐9‐yl)phenyl)spiro[1,8‐diazafluorene‐9,2′‐imidazole] (NFIP‐CZ) achieved efficient ultra‐deep‐blue emission (CIEx,y=0.1581, 0.0422) with the maximum external quantum efficiency (EQEmax), maximum current efficiency (CEmax) and maximum power efficiency (PEmax) of 11.94 %, 4.07 cd ⋅ A−1 and 2.56 lm ⋅ W−1. The record EQE is a breakthrough in both solution‐processed and vacuum vapor deposition ultra‐deep‐blue HLCT OLEDs currently.

Hybrid Local and Charge Transfer Emitters Utilizing Hyperconjugation Effect Towards Solution-Processed Ultra-Deep-Blue OLEDs with External Quantum Efficiency Approaching 12 .

Hybrid local and charge transfer (HLCT) excited state materials, which possess weak donor-acceptor (D-A) pure organic structures, deserve one of the most promising efficient and stable blue emitters. Through high-lying reverse intersystem crossing (hRISC) process, 75 % triplet excitons generated by electrical excitation could be harvested and utilized in organic light-emitting diodes (OLEDs). However, there are still significant challenges to achieve high-efficiency ultra-deep-blue HLCT emitters with low Commission Internationale de l'Eclairage (CIE) 1931 chromaticity coordinate y values. Here, a series of novel blue HLCT emitters based on spiro[1,8-diazafluorene-9,2'-imidazole] structure were designed and synthesized by fine-tuning the spiro[fluorene-9,2'-imidazole] core structure in our previous work through heteroatom substitution and hyperconjugation effect. The target emitters were endowed with excellent photophysical and electrochemical merits, thermal stability and solution processibility. The solution-processed OLED based on 4',5'-bis(4-(9H-carbazol-9-yl)phenyl)spiro[1,8-diazafluorene-9,2'-imidazole] (NFIP-CZ) achieved efficient ultra-deep-blue emission (CIEx,y=0.1581, 0.0422) with the maximum external quantum efficiency (EQEmax), maximum current efficiency (CEmax) and maximum power efficiency (PEmax) of 11.94 %, 4.07 cd ⋅ A-1 and 2.56 lm ⋅ W-1. The record EQE is a breakthrough in both solution-processed and vacuum vapor deposition ultra-deep-blue HLCT OLEDs currently.

Gold Coordination-Accelerated Multi-Resonance TADF Emission for Efficient Solution-Processible Ultrapure Deep-Blue OLEDs.

Multi-resonance (MR) type emitters have emerged as highly promising candidates for high-resolution organic light-emitting diodes (OLEDs). However, thermally activated delayed fluorescence (TADF) emissions with simultaneous short excited state lifetimes and ultrapure blue color (a CIEy close to 0.046 and an emission peak >440 nm) have rarely been obtained for MR emitters. Herein, we report a design of dual gold-coordinated MR molecules to achieve efficient and short-lived ultrapure blue TADF emission. The dinuclear Au(I) complex, namely iPrAuBN, shows a narrowband deep-blue emission with a peak maximum of 448 nm and a full width at half maximum (FWHM) of 29 nm in doped film. The coordination with two Au atoms significantly shortens the delayed fluorescence lifetime to 7.8 μs in comparison to 60.6 μs for the parental organic analogue. Solution-processed OLED doped with iPrAuBN demonstrates an ultrapure blue electroluminescence with a peak maximum of 442 nm, a FWHM of 19 nm, CIE coordinates of (0.154, 0.036), and a maximum external quantum efficiency of 14.8 %.

Efficient Deep-Blue Fluorescent OLEDs Based on a D-π-A Emitter Profiting From Intramolecular Hydrogen Bonds and a Hybridized Excited State.

High performance deep-blue emitters with a Commission International de l'Eclairage (CIE) coordinate of CIEy≤0.08 are highly desired in ultrahigh-definition displays. Herein, we designed and synthesized an efficient D-π-A deep-blue emitter, 2-(6-([1,1' : 3',1''-terphenyl]-5'-yl)pyridin-3-yl)-1-phenyl-1H-phenanthro[9,10-d] imidazole (mPTPH), using the synergistic effect of intramolecular hydrogen bond (H-bond) and hybridized excited state. Single-crystal structure analysis confirmed that there exist intra- and intermolecular H-bond interactions which could inhibit the structure vibration and increase photoluminescence efficiency. The photophysical and theoretical results show that mPTPH exhibited hybridized local and charge-transfer (HLCT) feature with strong deep-blue emission. Ultimately, the non-doped device based on mPTPH exhibited high maximum luminance of 20610 cd m-2. The doped device achieved high maximum external quantum efficiency of 5.4 % and small efficiency roll-off with deep-blue emission peak of 413 nm and CIE coordinate of (0.16, 0.08).

Modulating Charge-Transfer Excited States of Multiple Resonance Emitters via Intramolecular Covalent Bond Locking.

Advanced multiple resonance thermally activated delayed fluorescence (MR-TADF) emitters with high efficiency and color purity have emerged as a research focus in the development of ultra-high-definition displays. Herein, we disclose an approach to modulate the charge-transfer excited states of MR emitters via intramolecular covalent bond locking. This strategy can promote the evolution of strong intramolecular charge-transfer (ICT) states into weak ICT states, ultimately narrowing the full-width at half-maximum (FWHM) of emitters. To modulate the ICT intensity, two octagonal rings are introduced to yield molecule m-DCzDAz-BNCz. Compounds m-CzDAz-BNCz and m-DCzDAz-BNCz exhibit bright light-green and green fluorescence in toluene, with emission maxima of 504 and 513 nm, and FWHMs of 28 and 34 nm, respectively. Sensitized organic light-emitting diodes (OLEDs) employing emitters m-CzDAz-BNCz and m-DCzDAz-BNCz exhibit green emission with peaks of 508 and 520 nm, Commission Internationale de L'Eclairage (CIE) coordinates of (0.12, 0.65) and (0.19, 0.69), and maximum external quantum efficiencies (EQEs) of 30.2 % and 32.6 %, respectively.