Molecular Engineering of Push-Pull Diphenylsulfone Derivatives towards Aggregation-Induced Narrowband Deep Blue Thermally Activated Delayed Fluorescence (TADF) Emitters

Narrowband deep blue thermally activated delayed fluorescent (TADF) materials have attracted significant attention. Herein, four asymmetrical structured TADF emitters based on diphenylsulfone (DPS) acceptor and 9,9-dimethyl-9,10-dihydroacridine (DMAC) donor with progressive performances were developed. The tert-butyloxy auxiliary electron-donor was adopted to restrict the intramolecular rotations and provide efficient steric hindrance. Regioisomerization by altering the substitution position of DMAC on DPS unit further enhanced the intra- and inter-molecular interactions. The accompanying effects yielded increased energy level, minimized reorganization energy, and inhibited non-radiative transitions in the crystals of t BuO-SOmAD , which achieved narrowband deep-blue emission peaking at 424 nm (FWHM=64 nm, Φ_F=33.6 %) through aggregation-induced, blue-shifted emission (AIBSE). In addition, deep-blue organic light emitting diodes (OLEDs) based on t BuO-SOmAD realized the electroluminescence (EL) spectrum peaking located at 435 nm and CIE coordination of (0.12, 0.09).     

Effects of Electron Affinity and Steric Hindrance of the Trifluoromethyl Group on the π-Bridge in Designing Blue Thermally Activated Delayed Fluorescence Emitters

To explore the correlation of the acceptor electron affinity and the molecular conformation to the thermally activated delayed fluorescence (TADF) feature, a series of d -π-A molecules were designed and synthesized with triazine (Trz) as the acceptor (A) and carbazole (Cz) or tert-butylcarbazole (BuCz) as the donor (D). On the phenylene bridge between D and A, methyl or trifluoromethyl was incorporated close either to D or to A to tune the molecular conformation and the electron-withdrawing ability of acceptor. Both the twist angles and the singlet and triplet energy difference (ΔE_ST) were observed strongly dependent on the type and position of the substituent on the π-bridge. Only those molecules with trifluoromethyl locating close to the D side, namely TrzCz-CF₃ and TrzBuCz-CF₃, exhibit TADF feature, verifying that both sufficient electron affinity of the A unit and large dihedral angle between D and the π-bridge are necessary to ensure the occurrence of TADF. The blue organic light-emitting diodes fabricated with TrzCz-CF₃ and TrzBuCz-CF₃ achieved external quantum efficiencies of 9.40 % and 14.22 % with CIE coordinates of (0.19, 0.23) and (0.18, 0.29) respectively. This study provides practical design strategy for blue TADF materials particularly when planar and less crowded group is used as donor.     

New electron-donating segment to develop thermally activated delayed fluorescence emitters for efficient solution-processed non-doped organic light-emitting diodes

Thermally activated delayed fluorescent(TADF) materials capable of efficient solution-processed nondoped organic light-emitting diodes(OLEDs) are of important and practical significance for further development of OLEDs. In this work, a new electron-donating segment, 2,7-di(9 H-carbazol-9-yl)-9,9-dimethyl-9,10-dihydroacridine(2 Cz-DMAC), was designed to develop solution-processable non-doped TADF emitters. 2 Cz-DMAC can not only simultaneously increase the solubility of compounds and suppress har...     

Molecular Design Strategy of Thermally Activated Delayed Fluorescent Emitters Using CN‐Substituted Imidazopyrazine as a New Electron‐Accepting Unit

Thermally activated delayed fluorescence (TADF)‐based organic light‐emitting diodes (OLEDs) have attracted enormous attention recently due to their capability to replace conventional phosphorescent organic light‐emitting diodes for practical applications. In this work, a newly designed CN‐substituted imidazopyrazine moiety was utilized as an electron‐accepting unit in a TADF emitter. Two TADF emitters, 8‐(3‐cyano‐4‐(9,9‐dimethylacridin‐10(9H)‐yl)phenyl)‐2‐phenylimidazo[1,2‐a]pyrazine‐3‐carbonitrile (Ac‐CNImPyr) and 8‐(3‐cyano‐4‐(10H‐phenoxazin‐10‐yl)phenyl)‐2‐phenylimidazo[1,2‐a]pyrazine‐3‐carbonitrile (PXZ‐CNImPyr), were developed based on the CN‐substituted imidazopyrazine acceptor combined with acridine and phenoxazine donor, respectively. A CN‐substituted phenyl spacer was introduced between the donor and acceptor for a sufficiently small singlet‐triplet energy gap (ΔE_ST) and molecular orbital management. Small ΔE_ST of 0.07 eV was achieved for the phenoxazine donor‐based PXZ‐CNImPyr emitter. As a result, an organic light‐emitting diode based on the PXZ‐CNImPyr emitter exhibited a high external quantum efficiency of up to 12.7 %, which surpassed the EQE limit of common fluorescent emitters. Hence, the CN‐modified imidazopyrazine unit can be introduced as a new acceptor for further modifications to develop efficient TADF‐based OLEDs.     

Facile Generation of Thermally Activated Delayed Fluorescence and Fabrication of Highly Efficient Non-Doped OLEDs Based on Triazine Derivatives

A series of donor–acceptor–donor triazine-based molecules with thermally activated delayed fluorescence (TADF) properties were synthesized to obtain highly efficient blue-emitting OLEDs with non-doped emitting layers (EMLs). The targeted molecules use a triazine core as the electron acceptor, and a benzene ring as the conjugated linker with different electron donors to alternate the energy level of the HOMO to further tune the emission color. The introduction of long alkyl chains on the triazine core inhibits the unwanted intermolecular D –D/A–A-type π–π interactions, resulting in the intermolecular D–A charge transfer. The weak aggregation-caused quenching (ACQ) effect caused by the suppressed intermolecular D –D/A–A-type π–π interaction further enhances the emission. The crowded molecular structure allows the electron donor and acceptor to be nearly orthogonal, thereby reducing the energy gap between triplet and singlet excited states (ΔE_ST). As a result, blue-emitting devices with TH-2DMAC and TH-2DPAC non-doped EMLs showed satisfactory efficiencies of 12.8 % and 15.8 %, respectively, which is one of the highest external quantum efficiency (EQEs) reported for blue TADF emitters (λ_peak<475 nm), demonstrating that our tailored molecular designs are promising strategies to endow OLEDs with excellent electroluminescent performances.     

Quinoline-based aggregation-induced delayed fluorescence materials for highly efficient non-doped organic light-emitting diodes

Three new emitters,namely 10,10'-(quinoline-2,8-diyl)bis(10 H-phenoxazine)(Fene),10,10'-(quinoline-2,8-diyl)bis(10 H-phenothiazine)(Fens) and 10,10'-(quinoline-2,8-diyl)bis(9,9-dimethyl-9,10-dihydroacridine)(Yad),featuring quinoline as a new electron acceptor have been designed and conveniently synthesized.These emitters possessed small singlet-triplet splitting energy(ΔEst) and twisted structures,which not only endowed them show thermally activated delayed fluorescence(TADF)properties but also afforded a remarkable aggregation-induced emission(AIE) feature.Moreover,they also showed aggregation-induced delayed fluorescence(AIDF) property and good photoluminescence(PL) property,which are the ideal emitters for non-doped organic light-emitting diodes(OLEDs).Furthermore,high-performance non-doped OLEDs based on Fene,Fens and Yad were achieved,and excelle nt maximum external quantum efficiencies(EQE_(max)) of 14,9%,13.1% and 17,4%,respectively,were obtained.It was also found that all devices exhibited relatively low turn-on voltages ranging from 3.0 V to3.2 V probably due to their twisted conformation and the AIDF properties.These results demonstrated the quinoline-based emitters could have a promising application in non-doped OLEDs.     

Carbazole ring: A delicate rack for constructing thermally activated delayed fluorescent compounds with through-space charge transfer

Three carbazole derivatives, AcPTC, PxPTC and PtPTC, consisting of two 9,9-dimethyl-9,10-dihydroacridine, phenoxazine or phenothiazine donor groups and one diphenyltriazine acceptor group fixed at 1,8,9-positions of a single carbazole ring via phenylene, are designed and synthesized. X-ray diffraction analysis of AcPTC reveals that there exist multiple π-π interactions between the donor and acceptor groups to form a sandwich-like structural unit with edge-to-face interaction model. The compounds thus show obvious thermally activated delayed fluorescence with through-space charge transfer character and possess considerable photoluminescence quantum yields of up to 73% in doped films with sky-blue to yellow emissions. The solution-processed electroluminescent devices achieve the highest maximum external quantum efficiencies of 10.0%, 11% and 5.6% for AcPTC, PxPTC and PtPTC, respectively, with small efficiency roll-offs.     

Intermolecular Charge‐Transfer Transition Emitter Showing Thermally Activated Delayed Fluorescence for Efficient Non‐Doped OLEDs

A novel molecular model of connecting electron‐donating (D) and electron‐withdrawing (A) moieties via a space‐enough and conjugation‐forbidden linkage (D‐Spacer‐A) is proposed to develop efficient non‐doped thermally activated delayed fluorescence (TADF) emitters. 10‐(4‐(4‐(4,6‐diphenyl‐1,3,5‐triazin‐2‐yl) phenoxy) phenyl)‐9,9‐dimethyl‐9,10‐dihydroacridine (DMAC‐o‐TRZ) was designed and synthesized accordingly. As expected, it exhibits local excited properties in single‐molecule state as D‐Spacer‐A molecular backbone strongly suppress the intramolecular charge‐transfer (CT) transition. And intermolecular CT transition acted as the vital radiation channel for neat DMAC‐o‐TRZ film. As in return, the non‐doped device exhibits a remarkable maximum external quantum efficiency (EQE) of 14.7 %. These results prove the feasibility of D‐Spacer‐A molecules to develop intermolecular CT transition TADF emitters for efficient non‐doped OLEDs.     

Synthesis and properties of conjugated copolycondensates consisting of carbazole‐2,7‐diyl and fluorene‐2,7‐diyl

Carbazole and fluorene‐based random and alternating copolycondensates were synthesized to develop high‐performance blue light‐emitting polymers by improving electron injection ability of poly(N‐aryl‐2,7‐carbazole)s that showed intense blue electroluminescence (EL) with good hole‐injection and ‐transport ability. These copolycondensates absorbed light energy at about λ_max = 390 nm in CHCl₃ and 400 nm in film state, and fluoresced at about λ_max = 417 nm in CHCl₃ and 430 nm in the thin film state. Energy gaps between highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of them were about 2.9 eV, and the energy levels of LUMO situated lower than that of corresponding polycarbazole. Polymer light‐emitting diode devices having configuration of indium tin oxide/poly(3,4‐ethylenedioxythiophene)‐poly(styrenesulfonate)/polymer/CsF/Al using the copolycondensates, poly(N‐arylcarbazole‐2,7‐diyl), and poly(9,9‐dialkylfluorene‐2,7‐diyl), emitted bluish EL at operating voltages lower than 7 V. The device embedded the random copolycondensate showed notably higher performance with maximum luminance of 31,200 cd m^?2 at 11.0 V, and the current efficiencies observed under operating voltages lower than 7 V were higher than those of the other devices. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Pyridyl Pyrrolide Boron Complexes: The Facile Generation of Thermally Activated Delayed Fluorescence and Preparation of Organic Light‐Emitting Diodes

The electron positive boron atom usually does not contribute to the frontier orbitals for several lower‐lying electronic transitions, and thus is ideal to serve as a hub for the spiro linker of light‐emitting molecules, such that the electron donor (HOMO) and acceptor (LUMO) moieties can be spatially separated with orthogonal orientation. On this basis, we prepared a series of novel boron complexes bearing electron deficient pyridyl pyrrolide and electron donating phenylcarbazolyl fragments or triphenylamine. The new boron complexes show strong solvent‐polarity dependent charge‐transfer emission accompanied by a small, non‐negligible normal emission. The slim orbital overlap between HOMO and LUMO and hence the lack of electron correlation lead to a significant reduction of the energy gap between the lowest lying singlet and triplet excited states (ΔE_T‐S) and thereby the generation of thermally activated delay fluorescence (TADF).     

An efficient material via meta-position connection as thermally activated delayed fluorescence emitter for organic light-emitting diodes

A novel compound was designed and synthesized by connecting a dicyanobenzene acceptor and two 9,9-dimethyl-9,10-dihydroacridine donors to the 1,3,5-position of a phenyl ring by meta-position connection. This compound, which is a novel emitter for OLED devices, exhibits preferable heat stability. Moreover, the energy gap between its singlet and triplet states is as small as 0.04 eV, resulting in this molecule possesses thermally activated delayed fluorescence. Therefore, the corresponding device showed efficient electroluminescent performances. The maximum external quantum efficiency, maximum current efficiency, maximum power efficiency and maximum luminance were 16.5%, 40.8 cd A^?1, 45.8 lm W^?1 and 5120 cd m^?2, respectively. In addition, the CIE_x,y only changed from (0.22, 0.38) to (0.22, 0.39) over the entire operating voltage range, which confirms that the device possesses highly stable chromaticity with respect to the current density. Based on these experimental results, meta-connected type structures may provide a new approach for developing high-performance TADF emitters for OLED applications.     

Heavy-Atom-Free Bay-Substituted Perylene Diimide Donor-Acceptor Photosensitizers

Perylene diimide (PDI) dyes are extensively investigated because of their favorable photophysical characteristics for a wide range of organic material applications. Fine-tuning of the optoelectronic properties is readily achieved by functionalization of the electron-deficient PDI scaffold. Here, we present four new donor-acceptor type dyads, wherein the electron donor units – benzo[1,2-b : 4,5-b’]dithiophene, 9,9-dimethyl-9,10-dihydroacridine, dithieno[3,2-b : 2’,3’-d]pyrrole, and triphenylamine-are attached to the bay-positions of the PDI acceptor. Intersystem crossing occurs for these systems upon photoexcitation, without the aid of heavy atoms, resulting in singlet oxygen quantum yields up to 80 % in toluene solution. Furthermore, this feature is retained when the system is directly irradiated with energy corresponding to the intramolecular charge-transfer absorption band (at 639 nm). Geometrical optimization and (time-dependent) density functional theory calculations afford more insights into the requirements for intersystem crossing such as spin-orbit coupling, dihedral angles, the involvement of charge-transfer states, and energy level alignment.     

Molecular engineering on all ortho-linked carbazole/oxadiazole hybrids toward highly-efficient thermally activated delayed fluorescence materials in OLEDs

The highest efficiency thermally activated delayed fluorescence(TADF) emitters in OLEDs are mostly based on twisted donor/acceptor(D/A) type organic molecules.Herein,we report the rational molecular design on twisted all ortho-linked carbazole/oxadiazole(Cz/OXD) hybrids with tunable D-A interactions by adjusting the numbers of donor/acceptor units and electron-donating abilities.Singlet-triplet energy bandgaps(ΔE_(ST)) are facilely tuned from～0.4,0.15 to～0 eV in D-A,D-A-D to A-D-A type compounds.This variation correlates well with triplet-excited-state frontier orbital spatial separation efficiency.NonTADF feature with solid state photoluminescence quantum yield(PLQY)10% is observed in D-A type2 CzOXD and D-A-D type 4 CzOXD.Owing to the extremely low ΔE_(ST) for efficient reverse intersystem crossing,strong TADF with PLQY of 71%-92% is achieved in A-D-A type 4 CzDOXD and 4 tCzDOXD.High external quantum efficiency from 19.4% to 22.6% is achieved in A-D-A typed 4 CzDOXD and 4 tCzDOXD.     

Design Strategy of Decorating Phenylcarbazole with a Donor and Acceptor for Blue-Shifted Emission in Thermally Activated Delayed Fluorescent Emitters

A series of blue thermally activated delayed fluorescent (TADF) emitters of 1′′-(4,6-diphenyl-1,3,5-triazin-2-yl)-9,9′′-diphenyl-9H,9′′H-3,3′:9′,4′′-tercarbazole (TrzCz1) and 3′,6′-di-tert-butyl-1-(4,6-diphenyl-1,3,5-triazin-2-yl)-9-phenyl-9H-4,9′-bicarbazole (TrzCz2) were synthesized through a molecular design approach to decorate phenylcarbazole with a donor and an acceptor. The 1- and 4-positions of the phenylcarbazole core were modified with a diphenyltriazine acceptor and a bicarbazole or tert-butylcarbazole donor, respectively, through a synthetic strategy to introduce Br at the 1-position and F at the 4-position. The TrzCz1 and TrzCz2 emitters showed maximum photoluminescence emission bands at λ=443 and 433 nm, which were blueshifted relative to those of the corresponding TADF emitters with the same donor and acceptor, respectively. In the device application, the TrzCz1 emitter showed a maximum external quantum efficiency of 22.4 %, with a color coordinate of (0.16, 0.21), and the TrzCz2 emitter showed a maximum external quantum efficiency of 9.9 %, with a color coordinate of (0.14, 0.09). This work proved that the design strategy of decorating phenylcarbazole with a donor and an acceptor is effective at blueshifting the emission of TADF emitters.     

Synthesis and characterization of a new ethynyl‐linked alternating anthracene/fluorene copolymer for organic thin film transistor

A new p‐type conjugated copolymer, poly(9,10‐diethynylanthracene‐alt‐9,9‐didodecylfluorene) (PDADF), which is composed of ethynyl‐linked alternating anthracene/fluorene, is synthesized via a palladium(II)‐catalyzed Sonogashira coupling reaction with 9,10‐diethynylanthracene and 2,7‐diiodo‐9,9‐didodecyl‐fluorene. The obtained polymer is confirmed by FTIR, ¹H‐NMR, ¹³C‐NMR and elemental analysis. The PDADF had very good solubility in organic solvents such as chloroform and had a weight average molecular weight of 29,300 with a polydispersity index of 1.29. The PL maximum of the polymer was found at 533 and 568 nm for a solution and 608 nm for film, respectively. The highest occupied molecular orbital (HOMO) energy of the polymer is ?5.62 eV as measured via cyclic voltammetry (CV). A solution‐processed thin film transistor device showed a carrier mobility value of 6.0 × 10^?4 cm²/Vs with a threshold voltage of ?17 V and a capacitance (C_i) of 10 nF/cm². The out‐of‐plane and in‐plane GIXD pattern of spin‐coated polymer on SiO₂ dielectric surfaces showed an amorphous halo near 2θ = 20°. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1609–1616, 2009     

Potential of bifluorenylidene derivatives as nonfullerene small-molecule acceptor for heterojunction organic photovoltaics: a density functional theory study

To maximize the efficiency of heterojunction organic photovoltaics (HJOPVs), it is imperative to increase not only the open-circuit voltage (V _OC) but also the short-circuit current (I _SC). Therefore, it is desirable to find an organic acceptor material that possesses a higher lowest unoccupied molecular orbital (LUMO) level for higher V _OC and can absorb photons in the solar spectrum efficiently for larger I _SC. In this paper, in comparison with the typical donor poly(3-hexylthiophene) (P3HT) and acceptor [6,6]-phenyl-C₆₁-butyric acid ester ([60]PCBM), the geometries, electronic structures, absorption spectra, and transport properties of a series of organic compounds containing 9,9′-bifluorenylidene (9,9′BF) were systematically investigated using density functional and the semiclassical Marcus charge transfer theory calculation to evaluate their potential severing as acceptor. Our results indicate that the absorption spectra of 99′BF derivatives have better overlap with the solar spectrum than those of [60]PCBM, and higher LUMOs result in a significant enhancement of V _OC when they are used in HJOPVs with P3HT as donor materials. On the other hand, these compounds own higher electron carrier mobilities comparing with [60]PCBM. The study also demonstrates that the H-shaped compounds based on the 99′BF backbone possess good photophysical and charge transport properties, can be promising organic semiconductor for heterojunction photovoltaics.     

Donor–acceptor semiconducting polymers based on pyromellitic diimide

Three donor–acceptor copolymers P1 , P2 , and P3 with N,N′‐dodecylpyromellitic diimide as the electron‐acceptor unit with three diethynyl‐substituted donor monomers: 1,4‐diethynyl‐2,5‐bis(octyloxy)benzene, 2,7‐diethynyl‐9,9‐dioctyl‐9H‐fluorene, and 3,3′‐didodecyl‐5,5′‐diethynyl‐2,2′‐bithiophene have been synthesized by Sonogashira crosscoupling polymerization. The synthesized polymers showed deep highest occupied molecular orbital energy levels and larger band gaps (>2.5 eV). Polymers P1 , P2 , and P3 underwent fluorescence quenching with [6,6]‐phenyl‐C61‐butyric acid methyl ester (PCBM), indicating the intermolecular photo‐induced charge transfer between the donor polymers and the PCBM acceptor. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1617–1622     

Efficient deep-blue light-emitting polyfluorenes based on 9,9-dimethyl-9H-thioxanthene 10,10-dioxide isomers

We have designed and synthesized a series of deep-blue light-emitting polyfluorenes, PF-27SOs and PF-36SOs, by introducing electron-deficient 9,9-dimethyl-9H-thioxanthene 10,10-dioxide isomers (27SO and 36SO) into the poly(9,9-dioctylfluorene) (PFO) backbone. Compared with PFO, the resulting polymers exhibit an equivalent thermal decomposition temperature (>415 °C), an enhanced glass transition temperature (>99 °C), a decreased lowest unoccupied molecular orbital energy level (E_LUMO) below −2.32 eV, a blue-shifted photoluminescence spectra in solid film with a maximum emission at ~422 nm, and a shoulder peak at ~445 nm. The resulting polymers also show blue-shifted and narrowed electroluminescence spectra with deep-blue Commission Internationale de L'Eclairage (CIE) coordinates of (0.16, 0.07) for PF-27SO20 and (0.16, 0.06) for PF-36SO30, compared with (0.17, 0.13) for PFO. Moreover, simple device based on PF-36SO30 achieves a superior device performance with a maximum external quantum efficiency (EQE_max = 3.62%) compared with PFO (EQE_max = 0.47%). The results show that nonconjugated 9,9-dimethyl-9H-thioxanthene 10,10-dioxide isomers can effectively perturb the conjugation length of polymers, significantly weaken the charge-transfer effect in donor–acceptor systems, substantially improve electroluminescence device efficiency, and achieve deep-blue light emission.     

Synthesis and electroluminescent performance of thermally activated delayed fluorescence‐conjugated polymers with simple formylphenyl as pendant acceptor

Formylphenyl has been demonstrated to act as an acceptor to construct thermally activated delayed fluorescence (TADF) emitter, and therefore a series of the TADF‐conjugated polymers with formylphenyl as pendant acceptor and carbazole/acridine as backbone donor are designed and synthesized. All polymers involve the twisted donor/acceptor structural moieties with the sufficiently spatial separation between the highest occupied molecular orbital and the lowest unoccupied molecular orbital as well as a small singlet/triplet splitting, and exhibit the legible TADF features confirmed by theoretical calculation and their transient decay spectra. The solution‐processed organic light‐emitting diodes using neat film of the polymers as emissive layer achieve excellent performance with the maximum external quantum efficiency (EQE) of up to 10.6%, the maximum current efficiency of up to 35.3 cd A⁻¹ and the low turn‐on voltage of 2.7 V. Moreover, the EQE still remains 10.3% at the luminance of 1000 cd m⁻² with the low driving voltage of 4.4 V and extremely small efficiency roll‐off. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 1989–1996     

High Power Efficiency Blue‐to‐Green Organic Light‐Emitting Diodes Using Isonicotinonitrile‐Based Fluorescent Emitters

Herein, 9,10‐dihydro‐9,9‐dimethylacridine (Ac) or phenoxazine (PXZ)‐substituted isonicotinonitrile (INN) derivatives, denoted as 2AcINN , 26AcINN , and 26PXZINN , were developed as a series of thermally activated delayed fluorescence (TADF) emitters. These emitters showed reasonably high photoluminescence quantum yields of 71–79 % in the host films and high power efficiency organic light‐emitting diodes (OLEDs). Sky‐blue emitter 26AcINN exhibited a low turn‐on voltage of 2.9 V, a high external quantum efficiency (η _ext) of 22 %, and a high power efficiency (η _p) of 66 lm W⁻¹ with Commission Internationale de l′Eclairage (CIE) chromaticity coordinates of (0.22, 0.45), whereas green emitter 26PXZINN exhibited a low turn‐on voltage of 2.2 V, a high η _ext of 22 %, and a high η _p of 99 lm W⁻¹ with CIE chromaticity coordinates of (0.37, 0.58). These performances are among the best for TADF OLEDs to date.