Solid-state Emission Research Articles

Multicomponent Diversity-Oriented Access to Boronic-Acid-Derived Pyrrolide Salicyl-Hydrazone Fluorophores with Strong Solid-State Emission.

Fluorescent molecular platforms are highly sought after for their applications in biology and optoelectronics but face challenges with solid-state emission quenching. To address this, bulky substituents or aggregation-induced emission luminogens to restrict intramolecular motion are used to enhance the brightness. Here, we have successfully engineered a novel class of boron complexed pyrrolide salicyl-hydrazone fluorophores named BPSHY. These dyes were synthesized through a diversity-oriented condensation of pyrrole and salicylaldehyde derivatives combined with various aromatic boronic acids. The resulting 3D structures, owing to bulky boron axially substituted aryl groups, impart excellent solubility in a variety of solvents. Significantly, the BPSHY dyes exhibit strong absorption in the visible region and remarkably large Stokes shifts. Crucially, they demonstrate intense emission in aqueous solutions due to aggregation-induced emission effects. In solid-states, these dyes achieve high quantum yields, reaching up to 58%. Further expanding their utility, we developed two new BPSHY probes: one incorporating morpholine and another containing triphenylphosphine salt. Both of them are found to specifically label subcellular organelles such as lysosomes and mitochondria within live cells. Notably, these probes demonstrate exceptional staining efficacy and two-photon fluorescence feature. This highlights the considerable promise of BPSHY fluorophores for monitoring and visualizing the dynamic transformations of organelles.

Sterically Tuned Ortho-Phenylene-Linked Donor-Acceptor Benzothiazole-Based Boron Difluoride Complexes as Thermally-Activated Delayed Fluorescence Emitters for Organic Light-Emitting Diodes.

Two donor-acceptor dyes with an ortho-phenylene-linked carbazole electron donor and a benzothiazole-fused boron heterocyclic acceptor were designed, synthesized, and spectroscopically investigated. Due to the steric effects of boron heterocyclic units, the dyes demonstrate different conformations in the crystalline state. The presence of numerous hydrogen-bonding intermolecular interactions and the very weak π-π stacking in the molecular packing results in intense solid-state emission with photoluminescence quantum yields of 40 and 18% for crystals and 50 and 42% for host-based light-emitting layers. The compounds show aggregation-induced emission and thermally activated delayed fluorescence (TADF). The received ionization potential and electron affinity values suggested good charge-injecting ability and bipolar charge-transporting properties of the developed dyes. Transport of holes and electrons was detected in layers of one dye by the time-of-flight measurements. The benzothiazole-based boron difluoride complexes showed high electron mobility of 1.5 × 10-4 and 0.7 × 10-4 cm2 V-1 s-1 at an electric field of 1.35 × 106 V cm-1. Therefore, these dyes were successfully applied as emitters in organic light-emitting diodes with external quantum efficiencies of 15 and 13%, respectively. Our study marks a critical advancement in the area of solid-state emissive boron difluoride dyes, which can be applied as TADF emitters into organic light-emitting diodes. The obtained results reveal that the orientation of the acceptor unit in the ortho-phenylene-linked donor-acceptor dyes makes a significant impact on the TADF activity.

Benzodifuranone Crystals with Solid-State Emission Arising from the Introduction of Bulky Substituents.

Benzodifuranone derivatives, structural analogues of widely studied diketopyrrolopyrrole, have been reported to show photoluminescence exclusively in solution states. Here, upon introducing bulky aromatic groups into benzodifuranone dyes, crystals with unprecedented solid-state emission were obtained. A crystallographic analysis revealed that the emissive properties should most likely be attributed to the absence of stacking between the dye scaffolds. In addition to the solid-state emission, the compound showed responsivity to external stimuli, i. e., luminescent mechanochromism and thermosalient effect.

New AIEgens based on thieno[2,3-d]pyrimidine derivatives: Synthesis, DFT calculations, and molecular docking

In this paper, new thieno[2,3-d]pyrimidine analogs have been synthesized and characterized through different spectroscopic techniques. The photophysical properties of the molecules (7b-7f) and the quantum chemical calculations have been investigated. These molecules exhibited aggregation-induced emission behavior and showed efficient emission in both solid and solution states. A shift toward shorter wavelengths (hypsochromic shift) was observed when transitioning from the solution to the solid state, which could be explained by photoinduced intramolecular charge transfer (ICT) processes. DFT calculations confirmed that the diverse behavior of the thieno[2,3-d]pyrimidine analogs could be attributed to variations in molecular packing and rigidity. This study illustrates how luminophores aggregation can occur without significantly impacting the excited state, emphasizing the unconventional behavior resulting from minor alterations in terminal substituents. These findings hold implications for the advancement of luminescent materials. Additionally, theoretical calculations were conducted to compare the excitations and emissions of the new AIEgens with practical observations. Furthermore, a molecular docking study of the five AIEgens suggested their potential utility as anticancer drugs. Compound 7c exhibited a high affinity for human cyclin-dependent kinase 2 (CDK-2) protein, with a binding energy of 9.6 kcal/mol, indicating its potential as an inhibitor for this specific protein.

Synthesis of quadruply boron-doped acenes with stimuli-responsive multicolor emission

Boron-doped acenes have attracted attention due to their unique structures and intriguing luminescent properties. However, the hitherto known boron-doped acenes have only one or two boron atoms, limiting the chemical space of this unique family of compounds and the capability to tune their optical properties. Herein, we report the synthesis of quadruply boron-doped acenes, including pentacene, heptacene, and nonacene. The importance of the boron doping level on the luminescent properties of acenes is demonstrated. The title compounds manifest enhanced Lewis acidity as compared with dihydrodiboraacenes, leading to Lewis-base-responsive emission in the solid state. Moreover, quadruply boron-doped nonacene displays mechanochromic luminescence in addition to Lewis-base-responsive properties, realizing high-contrast solid-state multicolor emission. This work greatly expands the chemistry of boron-doped acenes and offers opportunities for developing boron-based luminescent materials.

The Solid-State Multi-Color Fluorescence Switching from a [2.2]Paracyclophane-Based Triarylborane.

The fluorophores, the fluorescence of which can be switched between multi bright colors in the solid state, show promising applications not only in the sophisticated multicolor display but also in the advanced encryption and anti-counterfeiting systems. However, it is very challenging to obtain such fluorophores. Herein, we disclose such an example, g-BPhANMe2-Cp, which contains an electron-donating dimethylamino (NMe2) and an electron-accepting [(2-dimesitylboryl)phenyl]acetyl at the pseudo-gem position of [2.2]paracyclophane skeleton. This molecule can display tricolor mechanochromic luminescence (MCL) due to the different responses of the mechanically ground amorphous state to heating and solvent-fuming. Owing to the absence of intermolecular π-π interactions in the solid state, the fluorescence efficiency is very high irrespective of its morphological state (ΦF=0.60-0.87). Moreover, this molecule also displays reversible acidochromic luminescence (ACL) by protonation and deprotonation of NMe2 with trifluoroacetic acid (TFA) and triethylamine (TEA), respectively. The protonated sample fluoresces (ΦF=0.31) at much shorter wavelength due to the interruption of intramolecular charge transfer process. Therefore, with the combination of tricolor MCL and ACL properties, the solid-state emission of g-BPhANMe2-Cp can be switched among four bright fluorescence colors of yellow, green, cyan and blue via treatment with appropriate stimulus.

Synthesis, Characterization and pH-sensitivity of AIE Emitters Obtained by RAFT Polymerization of Pt(II) Pincer Complexes with Polyvinylpyrrolidon

Two phosphine substituted Pt(II) pincer complexes (Pt1 and Pt2) containing NNC ligands: methyl 6-phenyl-[2,2'-bipyridine]-5-carboxylate (C1) and methyl 6-(4-fluorophenyl)-[2,2'-bipyridine]-5-carboxylate (C2), and diphenyl(vinyl)phosphine were obtained and characterized using mass spectrometry, NMR spectroscopy and XRD crystallography. The complexes are weakly phosphorescent in acetonitrile solution but display stronger emission in solid state, which is critically determined by the mode of molecular packing in crystal cell. Pt1 and Pt2 readily take part in RAFT copolymerization with polyvinylpyrrolidon to give amphiphilic P1 and P2 copolymers containing 6-7 and 3-5 units of the corresponding complexes in the polymeric chains. In DMFA, P2 forms nanospecies where the platinum chromophores aggregate to give strong emission red shift compared to the monomeric complexes due to Pt-Pt bonding in the aggregates. In aqueous solutions P1 and P2 form micelles with the hydrophobic core containing aggregated platinum chromophores emitting in the NIR spectral region. Hydrolysis of the ester group in the NNC ligand in P2 gives a water-soluble phosphorescent emitter with high lifetime sensitivity to pH in biologically relevant interval (pKa = 6.06).

Wet-spinning fabrication of stretchable multicolor fluorescent fibers augmented with dual-state emissive dyes

Flexible luminous fibers have attracted wide attention in the field of functional and smart textiles. In this work, stretchable multicolor fluorescent fibers were successfully prepared by wet-spinning using thermoplastic polyurethane (TPU) and the boron ketoimine fluorophores (TPA-BKI dyes). Due to the donor (D)-acceptor (A) push-pull electronic system and highly twisted triphenylamine (TPA) skeleton, TPA-BKI dyes exhibited bright emission in both solution and solid states. Meanwhile, the polymer chains further improved the emission efficiency of TPA-BKI dyes in TPU matrix by avoiding close contact between dye molecules, as well as preventing intramolecular rotations in the excited states. Wet-spinning can be used for large-scale and continuous preparation of fluorescent fibers. The TPA-BKI/TPU fibers showed excellent flexibility, high mechanical strength, and bright multicolor fluorescent emission (green, yellow, and red, respectively) when the dye content was as low as 0.1 wt%. Overall, the feasibility of large-scale preparation of fluorescent fibers and their excellent properties, such as flexibility, multicolor fluorescence, and mechanical stability, make them suitable for potential applications, including clothing displays, fashion designs, security, and anti-counterfeiting.

Exciton Dissociation and Recombination Afford Narrowband Organic Afterglow Through Efficient FRET.

Organic afterglow with long-persistent luminescence (LPL) after photoexcitation is highly attractive, but the realization of narrowband afterglow with small full-width at half-maximum (FWHM) is a huge challenge since it is intrinsically contradictory to the triplet- and solid-state emission nature of organic afterglow. Here, narrow-band, long-lived, and full-color organic LPL is realized by isolating multi-resonant thermally activated delayed fluorescent (MR-TADF) fluorophores in a glassy steroid-type host through a facile melt-cooling treatment. Such prepared host becomes capable of exciton dissociation and recombination (EDR) upon photoirradiation for both long-lived fluorescence and phosphorescence; and, the efficient Förster resonance energy transfer (FRET) from the host to various MR-TADF emitters leads to high-performance LPL, exhibiting small FWHM of 33nm, long persistent time over 10s, and facile color-tuning in a wide range from deep-blue to orange (414-600nm). Moreover, with the extraordinary narrowband LPL and easy processability of the material, centimeter-scale flexible optical waveguide fibers and integrated FWHM/color/lifetime-resolved multilevel encryption/decryption devices have been designed and fabricated. This novel EDR and singlet/triplet-to-singlet FRET strategy to achieve excellent LPL performances illustrates a promising way for constructing flexible organic afterglow with easy preparation methods, shedding valuable scientific insights into the design of narrow-band emission in organic afterglow.

Suzuki-Miyaura coupling reaction: Blue-yellow emitting AIE active dyes for organic electronics

A series of eight novel donor‒acceptor (D─A) based 2,3-di(thiophen-2-yl)quinoxaline derivatives 2–9 were prepared by modulating donor species on quinoxaline core with Palladium catalyzed Suzuki–Miyaura ‘C–C bond’ coupling reaction. The synthesized molecules were fully characterized and studied for impact of D–A interaction on opto-electrochemical properties. Absorption spectra of 2–9 display intramolecular charge transfer (ICT) transitions in the range of 388–414 nm. Dyes shows positive solvatochromism and emit in blue‒yellow region with emission maxima 444−550 nm on excitation at their respective ICT maxima in toluene, chloroform, DCM, DMSO and neat solid film. Further, solid state emission was studied for aggregation‒induced emission (AIE) effect in THF–water system due to the nanoparticles formation, as confirmed by FEG‒SEM technique. The HOMO and LUMO energy level for compounds 2–9 were measured by cyclic voltammetry and found in the range of −5.15 to −5.94 eV and −2.81 to −3.39 eV. Theoretical studies of molecules were also carried out by using DFT and TD‒DFT calculations. The comparable HOMO and LUMO energy levels with reported ambipolar materials and efficient solid-state emission make synthesized compounds potential candidate for solid state emissive, ambipolar charge transporting materials in organic electronics.

The optical properties of 3 + 3 macrocyclic Schiff base thin material obtained by the Molecular Beam Epitaxy method

3 + 3 optically active macrocyclic Schiff bases were synthesized in the reaction between 4-tert-butyl-2,6-diformylphenol with (1R,2R)-(+)-1,2-diphenylethylenediamine (S1) or (1S,2S)-(−)-1,2-diphenylethylenediamine (S1a). The new compounds were spectroscopically characterised by NMR, IR, X-ray (S1a), UV–Vis and fluorescence spectroscopy. The S1a molecule creates channels with distances between oxygen atoms ranging from 5.8-6.3 Å and sufficiently large to host acetonitrile molecule. Both compounds exhibit green-yellow emission in solution and solid state. Thin layers of the S1 compound obtained via Molecular Beam Epitaxy (MBE) were characterised by scanning electron microscopy with energy-dispersive X-ray spectroscopy SEM/EDS and atomic force microscopy (AFM). The optical properties of the S1/Si thin material were analysed using spectroscopic ellipsometry (SE), fluorescence spectroscopy and synchrotron radiation (SR). The time constant for the decay investigated under SR, denoted by τ1, was determined to be approximately 1.02 ns, suggesting a fast deactivation process of the excited electronic state in the S1/Si material. The ellipsometric analysis of the S1/Si layer showed semiconducting behaviour with pronounced absorption features in the UV range, attributed to π → π* and n → π* transitions, characteristic of Schiff bases. The band-gap energy, determined using the Tauc method, is 3.46 ± 0.01 eV. These analyses highlight the material’s potential in applications requiring precise control of optical properties. In the emission spectrum of S1a, a significant emission peak of approximately 561 nm indicates the presence of a prominent emissive process within this wavelength. The S1a compound is emissive in the yellow-green region of the spectrum and has a longer decay time, which suggests that it can be used in sensing optical technologies.

Triphenylamine-Based Solid-State Emissive Fluorene Derivative with Aggregation-Induced Emission Enhancement Characteristics

Aggregation-induced emission (AIE) has garnered considerable attention in recent years. Understanding the mechanisms underlying AIE phenomena is crucial. Here, we present the design and synthesis of a novel fluorene derivative (4) based on triphenylamine, which exhibits typical AIE properties. The structure of it was totally characterized using FT-IR, MALDI-TOF mass analysis, elemental analysis, 1H, and 13C NMR spectroscopy. It displayed strong solid-state emission with diverse fluorescence characteristics. The AIE property of the compound was systematically studied using photoluminescence spectroscopy, revealing a distinct yellow light-emitting phenomenon. The solid-state luminescence showed a red shift of 148 nm compared to its luminescence in dilute dimethylformamide (DMF) solutions. Moreover, photophysical characteristics, including absorption and emission spectra, as well as fluorescence lifetime, were examined using UV–vis absorption and fluorescence emission spectroscopy. Compound (4) exhibited superior photosensitization abilities in both solid and solution states, with a notably enhanced effect observed in the solid state compared to the solution state.

Achieving Controllable Thermochromic Fluorescence via Synergistic Intramolecular Charge Transfer and Molecular Packing

Thermochromic fluorescent materials (TFMs) have attracted significant attention due to their unique fluorescent colorimetric response to temperature. However, existing TFMs still suffer from weak stimulus responsiveness, broad temperature response ranges, uncontrollable emission color changes, and low quantum yields. In this study, we address these issues by designing and synthesizing three diketone‐boron complexes with distinct emission wavelengths (NWPU‐(2‐4)). Utilizing a molecular engineering strategy to manipulate intramolecular charge transfer transitions and molecular packing modes, our synthesized complexes exhibit efficient fluorescence emission in both solution and solid states. Moreover, their emission wavelengths are highly sensitive to environmental polarity. By incorporating these compounds into thermosensitive matrices of long‐chain alkanes, we produced TFMs with varied fluorescence emission peak variation ranges. Notably, the TFM based on NWPU‐4, owing to its strong charge transfer transitions and dense J‐aggregate packing configuration, not only exhibits intense fluorescence emission spanning the deep red to near‐infrared spectrum but also displays a remarkable 90 nm broad range of thermochromic properties. Ultimately, it was successfully applied to programmable, thermally controlled, multi‐level information encryption.

Achieving Controllable Thermochromic Fluorescence via Synergistic Intramolecular Charge Transfer and Molecular Packing.

Thermochromic fluorescent materials (TFMs) have attracted significant attention due to their unique fluorescent colorimetric response to temperature. However, existing TFMs still suffer from weak stimulus responsiveness, broad temperature response ranges, uncontrollable emission color changes, and low quantum yields. In this study, we address these issues by designing and synthesizing three diketone-boron complexes with distinct emission wavelengths (NWPU-(2-4)). Utilizing a molecular engineering strategy to manipulate intramolecular charge transfer transitions and molecular packing modes, our synthesized complexes exhibit efficient fluorescence emission in both solution and solid states. Moreover, their emission wavelengths are highly sensitive to environmental polarity. By incorporating these compounds into thermosensitive matrices of long-chain alkanes, we produced TFMs with varied fluorescence emission peak variation ranges. Notably, the TFM based on NWPU-4, owing to its strong charge transfer transitions and dense J-aggregate packing configuration, not only exhibits intense fluorescence emission spanning the deep red to near-infrared spectrum but also displays a remarkable 90 nm broad range of thermochromic properties. Ultimately, it was successfully applied to programmable, thermally controlled, multi-level information encryption.

Incorporation of ESIPT into pillar[5]arene for solid-state dual emission responsive to n-hexane vapor

Abstract Pillar[5]arene is a promising macrocyclic receptor of a chemical sensor showing shape-selective encapsulation of neutral molecules into the cavity, but the poor fluorescence properties remain a challenge. Herein, we report a pillar[5]arene coupled with 2-(2-hydroxyphenyl)benzoxazole (HBO), which displays bright fluorescence in both solution and the solid state. Owing to the excited-state intramolecular proton transfer (ESIPT) in the HBO moiety, greatly improved fluorescence is observed for the pillar[5]arene derivative in CHCl3 (Φlum = 11%) and powder form (Φlum = 25%). Moreover, the emission color changes from light green to blue when the powder sample is exposed to n-hexane vapor. The color change derives from variable dual emission via ESIPT and excimer-forming pathways, as suggested by fluorescence lifetime measurements at different wavelengths. Powder x-ray diffraction indicates that increased crystallinity and a small alteration in the solid-state structure leads to visible fluorescent chromism upon vapor encapsulation.

Tetra dansylamides substituted cyclen and cyclam macrocycles as fluorescent sensing probes for metal ions and temperature-responsive materials in dopped polymers

Two novel tetra-dansyl derivatives incorporating cyclen (1,4,7,10-tetraazacyclododecane) and cyclam (1,4,8,11-tetraazacyclotetradecane) macrocycles have been synthesized, thoroughly characterized, and their photophysical properties examined, both in solution and in the solid state. These compounds exhibit fluorescence emission with quantum yields up to 40 %, varying significantly with different solvents. They also display positive solvatofluorochromic behavior, with emissions ranging from green to yellow colours. Kamlet-Taft studies were conducted to better understand solute-solvent interactions. Furthermore, aggregation-induced emission was observed in solutions with high water content, confirmed via dynamic light scattering. Given the intrinsic properties of these compounds, their potential for environmental remediation was explored through metal ion sensing studies. Compounds L1 and L2 demonstrated high sensitivity to Cu2+ and Hg2+ ions, significantly modulating their emission, with L2 capable of detecting and quantifying Hg2+ concentrations as low as 2–3 μM. Additionally, the solid-state emission of these compounds encouraged an investigation into their potential as temperature sensors. Several doped polymer thin films were fabricated, establishing a linear relationship with temperature beyond their melting point. These findings suggest that these tetra-chromophoric compounds hold promise as molecular thermometers.

Regulating the photoluminescence of aluminium complexes from non-luminescence to room-temperature phosphorescence by tuning the metal substituents

Although luminescent aluminum compounds have been utilized for emitting and electron transporting layers in organic light-emitting diodes, most of them often exhibit not phosphorescence but fluorescence with lower photoluminescent quantum yields in the aggregated state than those in the amorphous state due to concentration quenching. Here we show the synthesis and optical properties of β-diketiminate aluminum complexes, such as crystallization-induced emission (CIE) and room-temperature phosphorescence (RTP), and the substituent effects of the central element. The dihaloaluminum complexes were found to exhibit the CIE property, especially RTP from the diiodo complex, while the dialkyl ones showed almost no emission in both solution and solid states. Theoretical calculations suggested that undesired structural relaxation in the singlet excited state of dialkyl complexes should be suppressed by introducing electronegative halogens instead of alkyl groups. Our findings could provide a molecular design not only for obtaining luminescent complexes but also for achieving triplet-harvesting materials.

Ligand Controls Excited Charge Carrier Dynamics in Metal-Rich CdSe Quantum Dots: Computational Insights.

Small metal-rich semiconducting quantum dots (QDs) are promising for solid-state lighting and single-photon emission due to their highly tunable yet narrow emission line widths. Nonetheless, the anionic ligands commonly employed to passivate these QDs exert a substantial influence on the optoelectronic characteristics, primarily owing to strong electron-phonon interactions. In this work, we combine time-domain density functional theory and nonadiabatic molecular dynamics to investigate the excited charge carrier dynamics of Cd28Se17X22 QDs (X = HCOO-, OH-, Cl-, and SH-) at ambient conditions. These chemically distinct but regularly used molecular groups influence the dynamic surface-ligand interfacial interactions in Cd-rich QDs, drastically modifying their vibrational characteristics. The strong electron-phonon coupling leads to substantial transient variations at the band edge states. The strength of these interactions closely depends on the physicochemical characteristics of passivating ligands. Consequently, the ligands largely control the nonradiative recombination rates and emission characteristics in these QDs. Our simulations indicate that Cd28Se17(OH)22 has the fastest nonradiative recombination rate due to the strongest electron-phonon interactions. Conversely, QDs passivated with thiolate or chloride exhibit considerably longer carrier lifetimes and suppressed nonradiative processes. The ligand-controlled electron-phonon interactions further give rise to the broadest and narrowest intrinsic optical line widths for OH and Cl-passivated single QDs, respectively. Obtained computational insights lay the groundwork for designing appropriate passivating ligands on metal-rich QDs, making them suitable for a wide range of applications, from blue LEDs to quantum emitters.

Multiple-stimuli fluorescent responsive metallo-organic helicated cage arising from monomer and excimer emission

Effectively regulating monomer and excimer emission in a singular supramolecular luminous platform is challenging due to high difficulty of precise control over its aggregation and dispersion behavior when subjected to external stimuli. Here, we show a metallo-cage (MTH) featuring a triple helical motif that displays a unique dual emission. It arises from both intramolecular monomer and intermolecular excimer, respectively. The distorted molecular conformation and the staggered stacking mode of MTH excimer are verified through single crystal X-ray diffraction analysis. These structural features facilitate the switch between monomer and excimer emission, which are induced by changes in concentration and temperature. Significantly, adjusting the equilibrium between these two states in MTH enables the production of vibrant white light emission in both solution and solid state. Moreover, when combined with a PMMA (polymethyl methacrylate) substrate, the resulting thin films can serve as straightforward fluorescence thermometer and thermally activated information encryption materials.

Dicyanoimidazole-based organic small molecule fluorophores: Synthesis and luminescent properties

Four new organic D-π-A fluorophores consisting of different electron donors (carbazole and diphenylamine) and acceptors (4,5-dicyanoimidazole and 5,6-dicyanobenzo[d]imidazole), i.e., DCI-Cz, DCI-TPA, DCBI-Cz and DCBI-TPA, were synthesized to obtain deep-blue organic light-emitting diodes (OLEDs). These compounds exhibited good solubility and excellent thermal stability as well as strong deep-blue and blue emission in solution and solid states. With mCP (1,3-di(9H-carbazol-9-yl)benzene) as the host material, the doped devices with a configuration of ITO/PEDOT:PSS (30 nm)/mCP:dopant (x wt%) (25 nm)/TPBi (35 nm)/Liq (2 nm)/Al (150 nm) were fabricated by solution-processing the emitting layers to evaluate their electroluminescence (EL) performances. The devices using the blend of mCP with DCI-TPA as emitting layers exhibited the best electroluminescent performance with a maximum external quantum efficiency (EQEmax) of 4.39 % and a maximum current efficiency of 3.04 cd/A.