Efficient Thermally Activated Delayed Fluorescence Research Articles

Multireference Ab Initio Calculations on Excited Electronic States of Carbazole-Based Organic Compounds for Thermally Activated Delayed Fluorescence.

The emerging technology of organic light-emitting diodes takes advantage of the thermally activated delayed fluorescence (TADF) mechanism for improved efficiency. Carbazole-based organic molecules are suitable for TADF emission because of charge transfer excitations between the electron-donor carbazole and an electron-acceptor unit. Computational design of new TADF molecules with the desired properties is challenging because charge-transfer excitations cannot be predicted accurately by time-dependent density functional theory. Four groups of carbazole-based donor-acceptor molecules have been studied using multireference ab initio methods to understand the nature of excited electronic states. The state-averaged complete active space self-consistent field (SA-CASSCF) and the N-electron valence state perturbation theory (NEVPT2) were used to calculate energies and oscillator strengths for multiple excited electronic states. The number of active electrons and orbitals and the number of excited states included in state-averaged CASSCF were selected such that the accuracy of ab initio predictions could be improved systematically. The procedure introduced here for the calculation of multiple excited electronic states of TADF candidates can be used to accelerate the computational search for efficient TADF materials.

Excited-State Engineering Enables Efficient Deep-Blue Light-Emitting Diodes Exhibiting BT.2020 Color Gamut.

Organic luminescent materials that exhibit thermally activated delayed fluorescence (TADF) can convert non-emissive triplet excitons into emissive singlet states through a reverse intersystem crossing (RISC) process. Therefore, they have tremendous potential for applications in organic light-emitting diodes (OLEDs). However, with the development of ultra-high definition 4K/8K display technologies, designing efficient deep-blue TADF materials to achieve the Commission Internationale de l'Éclairage (CIE) coordinates fulfilling BT.2020 remains a significant challenge. Here, an effective approach is proposed to design deep-blue TADF molecules based on hybrid long- and short-range charge-transfer by incorporation of multiple donor moieties into organoboron multiple resonance acceptors. The resulting TADF molecule exhibits deep-blue emission at 414nm with a full width at half maximum (FWHM) of 29nm, together with a thousand-fold increase in RISC rate. OLEDs based on the champion material achieve a record maximum external quantum efficiency (EQE) of 22.8% with CIE coordinates of (0.163, 0.046), approaching the coordinates of the BT.2020 blue standard. Moreover, TADF-assisted fluorescence devices employing the designed material as a sensitizer exhibit an exceptional EQE of 33.1%. This work thus provides a blueprint for future development of efficient deep-blue TADF emitters, representing an important milestone towards meeting the blue color gamut standard of BT.2020.

Achieving Deep‐Blue Through‐Space Charge‐Transfer Emitter by Designing the Donor‐π‐Donor‐σ‐Acceptor Molecular Structure

AbstractIn the realm of organic light‐emitting diode (OLED), through‐space charge transfer (TSCT) thermally activated delayed fluorescence (TADF) emitters have demonstrated remarkable achievements. Nevertheless, realizing both deep‐blue emission and high efficiency by the TSCT strategy remains a persistent challenge. Here, the novel donor‐π‐donor‐σ‐acceptor (D‐π‐D‐σ‐A) type deep‐blue TSCT emitter, namely D‐tCz‐BO, is formulated to investigate its performance in OLED. D‐tCz‐BO show a narrow deep‐blue emission and efficient TADF character (λPL = 448, FWHM = 54 nm, ΦPL = 82%, and ΔEST = 0.09 eV). More importantly, the OLED based on D‐tCz‐BO as the emitter showed a maximum external quantum efficiency (EQEmax) of 20.5%, with a Commission Internationale de l'Eclairage (CIE) coordinate of (0.14, 0.12). This represents one of the best deep‐blue TSCT‐TADF emitters to date.

Direct Comparative Studies Revealing the Contribution of TADF Activity of Organic Emitters Towards Efficient Electrochemiluminescence.

Electrochemiluminescence (ECL) featuring thermally activated delayed fluorescence (TADF) properties has attracted considerable interest, showcasing their potential for 100 % exciton harvesting, which marks a significant advancement in the realm of organic ECL. However, the challenge of elucidating the precise contribution of TADF to the enhanced ECL efficiency arises due to the lack of comparative studies of organic compounds with or without efficient TADF properties. In this study, we present four carbazole-benzonitrile molecules possessing similar chemical structures and comparable exchange energy (ΔEST). Despite their comparable properties, these compounds exhibited varying TADF efficiencies, warranting a closer examination of their underlying structural and electronic characteristics governing the optical properties. Consequently, intense ECL emission was only observed from 4CzBN with a remarkable TADF efficiency, underscoring the substantial difference in the ECL signal among molecules with comparable ΔEST and similar spectral properties but varying TADF activity.

Modulating the Locally Excited States with a Regulating Substituent for Highly Efficient Red/Near‐Infrared Thermally Activated Delayed Fluorescence Emitters

AbstractDeveloping highly efficient red/near‐infrared (NIR) thermally activated delayed fluorescence (TADF) materials is important for organic light‐emitting diodes (OLEDs). Here, two TADF emitters, APTT and APTI, which have the same D/A backbone but different attaching groups at acenaphtho‐[1,2‐b]pyrazine‐8,9‐dicarbonitrile (APDC) core, are reported. The appended regulating groups can not only suppress the D/A rotation due to the space confinement effects but also modulate the locally excited triplet state (3LE). The improved molecular rigidity suppresses the non‐radiative process, accounting for the improved photoluminescence quantum yields (PLQYs), while the modulated 3LE promotes the reverse intersystem crossing (RISC) process due to the high utilization efficiency of triplets. Consequently, both APTT and APTI demonstrate high PLQY and fast RISC process, thereby enhancing TADF efficiency. The doped devices based on APTT and APTI achieve maximum external quantum efficiency (EQEmax) values of 20.5% and 25.4% with emission peaks at 664 and 670 nm, respectively. The non‐doped devices of APTT and APTI achieve the EQEmax of 2.8% and 2.9% with emission peaks at 788 and 794 nm, respectively. Encouragingly, the non‐doped devices of APTI have set new records for near‐infrared TADF OLEDs based on the APDC core. This study provides an efficient approach to modulating the optoelectronic properties of highly efficient NIR TADF OLEDs.

Guest‐Induced Thermally Activated Delayed Fluorescence Organic Supramolcular Macrocycle Scintillators for High‐Resolution X‐Ray Imaging

AbstractOrganic scintillators, pivotal in security and medical applications, face challenges due to limited X‐ray absorption and exciton utilization. Herein, a novel class of organic scintillators is introduced, named guest‐induced thermally activated delayed fluorescence (TADF) within supramolecular macrocycles via host‐guest through‐space charge transfer (TSCT). Four co‐crystals are obtained through orthogonal crystallizations involving calix[3]acridan (C[3]A) and calix[3]phenothiazine (C[3]P) macrocycles as hosts, along with 1,2‐dicyanobenzene (DCB) and 4‐bromo‐1,2‐benzenedicarbonitrile (BrDCB) as guests. Interestingly, DCB@C[3]A and BrDCB@C[3]A co‐crystals exhibit strong host‐guest TSCT with reduced single‐triplet energy gap for efficient TADF emission, which leads to enhanced exciton utilization and X‐ray absorption, yielding radioluminescence intensities over 29 and 25 times higher than C[3]A. Similarly, substituting C[3]A with C[3]P, the obtained TADF co‐crystals also outperform C[3]P in scintillation performance. Additionally, the scintillation color of co‐crystals can be adjusted by varying the electron‐donating abilities of macrocycles and the electron‐accepting abilities of guests, offering a simpler color‐tuning mechanism than covalent‐bonded scintillators. Furthermore, the flexible film based on DCB@C[3]A exhibits promising application in X‐ray radiography, showcasing a high spatial resolution of 20 lp mm−1 @MTF = 0.77. The innovative strategy of fabricating organic scintillators via reversible non‐covalent interactions presents a novel solution for designing color‐tunable and high‐performance scintillators.

Through-Space Charge-Transfer-Based Aggregation-Induced Emission and Thermally Activated Delayed Fluorescence in Fused 2H-Chromene Coumarin Congener Generating ROS for Antiviral (SARS-CoV-2) Approach.

Harvesting triplets in metal-free organic frameworks at ambient conditions and finding appropriate applications are a formidable challenge. Herein, we report a donor-acceptor-type system composed of carbazole and fused 2H-chromene coumarin derivative, exhibiting triplet harvesting thermally activated delayed fluorescence (TADF) and aggregation-induced emission (AIE) behavior in solid and aggregated states, respectively. The presence of an sp3 linker and the introduction of a selected cyano/ester group in the acceptor result in twisted D-A architectures, further assisting in the suppression of nonradiative deactivation via through-space charge transfer and H-bonding interactions, fulfilling the stringent requirements for the simultaneous process of TADF and AIE, successively. Experimental and theoretical results revealed that the participation of the singlet/triplet charge transfer (1CT/3CT) and the higher lying hybrid triplet locally excited charge-transfer state (3LE + 3CT) leads to an efficient TADF. Both of the synthesized AIE-TADF congeners actively participated in the generation of reactive oxygen species (ROS) in nanoaggregate forms and were further explored computationally for antiviral prospects as inhibitors of the SARS-CoV-2 spike protein.

Rational molecular design of efficient yellow-red dendrimer TADF for solution-processed OLEDs: a combined effect of substitution position and strength of the donors

AbstractThe development of high-performance solution-processed red organic light-emitting diodes (OLEDs) remains a challenge, particularly in terms of maintaining efficiency at high luminance. Here, we designed and synthesized four novel orange-red thermally activated delayed fluorescence (TADF) dendrimers that are solution-processable: 2GCzBP, 2DPACzBP, 2FBP2GCz and 2FBP2DPACz. We systematically investigated the effect of substitution position and strength of donors on the optoelectronic properties. The reverse intersystem crossing rate constant (kRISC) of the emitters having donors substituted at positions 11 and 12 of the dibenzo[a,c]phenazine (BP) is more than 10-times faster than that of compounds substituted having donors substituted at positions 3 and 6. Compound 2DPACzBP, containing stronger donors than 2GCzBP, exhibits a red-shifted emission and smaller singlet-triplet energy splitting, ΔEST, of 0.01 eV. The solution-processed OLED with 10 wt% 2DPACzBP doped in mCP emitted at 640 nm and showed a maximum external quantum efficiency (EQEmax) of 7.8%, which was effectively maintained out to a luminance of 1,000 cd m−2. Such a device∙s performance at relevant display luminance is among the highest for solution-processed red TADF OLEDs. The efficiency of the devices was improved significantly by using 4CzIPN as an assistant dopant in a hyperfluorescence (HF) configuration, where the 2DPACzBP HF device shows an EQEmax of 20.0% at λEL of 605 nm and remains high at 11.8% at a luminance of 1,000 cd m−2, which makes this device one of the highest efficiency orange-to-red HF SP-OLEDs to date.

Positional isomeric effect: A simple and feasible strategy for constructing efficient red TADF materials

In order to investigate the effect of positional isomerization on the photoelectric properties of thermally activated delayed fluorescence (TADF) emitters, thereby fully stimulating the potential of the molecular backbone, herein, two red TADF isomers, oTPA-PPP and mTPA-PPP, were developed and synthesized by linking triphenylamine (TPA) donor into different positions of the pyrido [2′,3′:5,6] pyrazino [2,3-f] [1,10] phenanthroline (PPP). Their photoluminescent quantum yields (PLQYs) and external quantum efficiencies (EQEs) were significantly different by manipulating the substitution position of the donor. Compared with mTPA-PPP, oTPA-PPP exhibited higher PLQY benefiting from intramolecular hydrogen bonding and larger fluorescence radiative decay rate, as confirmed by both theoretical and experimental analyses. As a result, oTPA-PPP-based organic light-emitting diode (OLED) realized high EQEmax of 19.2 % with red emission at 603 nm, whereas mTPA-PPP achieves an EQEmax of 7.9 % at 596 nm. This work provides a simple and feasible molecular design strategy to design and select red TADF emitters with excellent properties.

Efficient Blue Thermally Activated Delayed Fluorescence Molecules with Sandwich‐Structured Through‐Space Charge Transfer for Fabricating High‐Performance OLEDs

AbstractExploring robust blue luminescent materials is of high significance but challenging for the commercialization application of organic light‐emitting diodes (OLEDs). In this work, it is wished to report two blue thermally activated delayed fluorescence (TADF) molecules with a through‐space charge transfer feature. They have sandwich‐structured molecular backbones comprised of one triphenyltriazine acceptor and two 9‐phenylcarbazole or 3,6‐di(tert‐butyl)‐9‐phenylcarbazole donors that are linked at the 1,8,9‐positions of a 3,6‐di(tert‐butyl)carbazole holder, and exhibit high thermal stability and strong blue delayed fluorescence with high photoluminescence quantum yields and fast reverse intersystem crossing. The blue OLEDs use 2TBCTC as an emitter and provide outstanding maximum external quantum efficiencies (EQEmaxs) of up to 32.76% with Commission Internationale de I'Eclairage coordinates of (0.160, 0.206). To the best of knowledge, 2TBCTC is the most efficient blue TADF emitter based on through‐space charge transfer in the literature. Moreover, the interlayer‐sensitizing OLED employs 2TBCTC as a sensitizer for blue multi‐resonance TADF (MR‐TADF) molecule (v‐DABNA) as guest emitter attains an excellent EQEmax of 32.69% with a narrow full width at half maximum of 18 nm, validating the excellent potential of 2TBCTC as sensitizer for MR‐TADF emitters and the feasibility and effectiveness of the interlayer sensitization strategy for blue hyperfluorescence OLEDs.

Introduction of a Chiral Biphenanthrene-Diol Unit to Achieve Circularly Polarized Thermally Activated Delayed Fluorescence.

Circularly polarized luminescence (CPL) materials are promising candidates for future display technology. However, such highly efficient emitters suffer from the issues of difficult chiral separation and low photoluminescence quantum yield (PLQY). In this work, the chiral 4,4'-biphenanthrene-3,3'-diol (BIPOL) unit was introduced into a thermally activated delayed fluorescence (TADF) framework for the first time. We presented two series of enantiomers, R/S-o-DCzBPNCN and R/S-p-DCzBPNCN, and the synthesis of enantiopure BIPOL can be prepared via normal column chromatography. Notably, o-DCzBPNCN showed narrow singlet-triplet gap of 0.05 eV, efficient TADF, and high PLQYs of 82 % in doped films. In addition, R/S-o-DCzBPNCN exhibited high luminescence dissymmetry factor (gPL ) values of -1.94×10-2 /+1.91×10-2 in doped films. The strategy of BIPOL introduction offers a new approach to organic emitters with stereospecific synthesis, TADF, and chiroptical properties.

A molecular descriptor of a shallow potential energy surface for the ground state to achieve narrowband thermally activated delayed fluorescence emission.

Narrowband thermally activated delayed fluorescence (TADF) molecules have extensive applications in optoelectronics, biomedicine, and energy. The full-width at half-maximum (FWHM) holds significant importance in assessing the luminescence efficiency and color purity of TADF molecules. The goal is to achieve efficient and stable TADF emissions by regulating and optimizing the FWHM. However, a bridge from the basic physical parameters (such as geometric structure and reorganization energy) to the macroscopic properties (delayed fluorescence, efficiency, and color purity) is needed and it is highly necessary and urgent to explore the internal mechanisms that influence FWHM. Herein, first-principles calculations coupled with the thermal vibration correlation function (TVCF) theory were performed to study the energy consumption processes of the excited states for the three TADF molecules (2,3-POA, 2,3-DPA, and 2,3-CZ) with different donors; inner physical parameters affecting the FWHM were detected. By analyzing the basic geometric and electronic structures as well as the transition properties and reorganization energies, three main findings in modulating FWHM were obtained, namely a large local excitation (LE) proportion in the first singlet excited state is advantageous in reducing FWHM, a donor group with weak electron-donating ability is beneficial for achieving narrowband emission, and small reorganization energies for the ground state are favorable for reducing FWHM. Thus, wise molecular design strategies to achieve efficient narrowband TADF emission are theoretically proven and proposed. We hope that these results will promote an in-depth understanding of FWHM and accelerate the development of high color purity TADF emitters.

Fully space-confined donor-acceptor interaction for highly efficient thermally activated delayed fluorescence emitters

The emerging through-space charge transfers (TSCT) emitters with thermally activated delayed fluorescence (TADF) have drawn increasing interest. However, the low luminescence efficiency and slow reverse intersystem crossing (RISC) always limit their device performances. A new molecular design strategy for TSCT-TADF emitters with a fully space-confined donor/acceptor conformation that integrates high luminescence efficiency and fast RISC is proposed herein. Two new TSCT-TADF emitters, TRZ-STFMe and TRZ-STFPh, are developed by introducing the methyl and phenyl substituents at the C2 of the rigid fluorene scaffold, respectively. The repulsive interaction between methyl and the acceptor induces a close and face-to-face donor–acceptor stacking to generate highly efficient TADF and suppress structural changes during the RISC process in TRZ-STFMe. In contrast, TRZ-STFPh shows relatively low luminescence efficiency and slow RISC because of its conformationally unstable phenyl substituent. With a high luminescence efficiency of 97 % and a significant RISC rate of 5.23 × 105 s−1, TRZ-STFMe demonstrates a high electroluminescence performance with a maximum external quantum efficiency (EQE) of 29.6 % and an EQE of 26.5 % at 1000 cd m−2.

Molecular Engineering Modulating the Singlet-Triplet Energy Splitting of Indolocarbazole-Based TADF Emitters Exhibiting AIE Properties for Nondoped Blue OLEDs with EQE of Nearly 20.

The development of efficient blue thermally activated delayed fluorescence (TADF) emitters with an aggregation-induced emission (AIE) nature, for the construction of organic light-emitting diodes (OLEDs), is still insufficient. This can be attributed to the challenges encountered in molecular design, including the inherent trade-off between radiative decay and reverse intersystem crossing (RISC), as well as small singlet-triplet energy splitting (ΔEST) and the requirement for high photoluminescence quantum yields (ΦPL). Herein, we present the design of three highly efficient blue TADF molecules with AIE characteristics by combining π-extended donors with different acceptors to modulate the differences in the electron-donating and electron-withdrawing abilities. This approach not only ensures high emission efficiency by suppressing close π-π stacking, weakening nonradiative relaxation, and enhancing radiative transition but also maintains the equilibrium ratio between the triplet and singlet excitons by facilitating the process of RISC. These emitters exhibit AIE and TADF properties, featuring quick radiative rates and low nonradiative rates. The ΦPL of these emitters reached an impressive 88%. Based on their excellent comprehensive performance, nondoped PICzPMO and PICzPMO OLEDs achieved excellent electroluminescence performance, exhibiting maximum external quantum efficiency (EQEmax) of up to 19.5%, while the doped device achieved a higher EQEmax of 20.8%. This work demonstrated that by fusing π-extended large rigid donors with different acceptors, it is possible to regulate the difference in electron-donating and electron-withdrawing abilities, resulting in a small ΔEST, high ΦPL, and fast RISC process, which is a highly feasible strategy for designing efficient TADF molecules.

Modulating excited state properties of thermally activated delayed fluorescence molecules by hybrid long-range and short-range charge transfer strategy

Balancing the rapid radiative decay process and the fast reverse intersystem crossing (RISC) process of thermally activated delayed fluorescence (TADF) molecule remains a great challenge and efficient molecular design strategies are highly desired. Herein, from a theoretical perspective, excited state properties of three reported TADF molecules (1TICz, 1BOICz and 2BOICz) are investigated based on density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations coupled with the thermal vibration correlation function (TVCF) method. Results indicate that, by introducing the multi-resonance (MR) acceptor, 1BOICz possesses hybrid long-range and short-range charge transfer features, balanced small energy gap (ΔEST) and large oscillator strength (f) is obtained. Furthermore, by incorporating double equivalent MR acceptors in 2BOICz, largely enhanced f with slightly changed ΔEST is achieved, inner mechanism for remarkable photophysical property is illustrated. Keep this strategy, seven new TADF molecules (2pDBA-bICz-1, 2pDBA-bICz-2, 2OSBA-bICz, 2DQAO-bICz, 2QAO-bICz, 2SQAO-bICz and 2OQAO-bICz) are theoretically designed, detailed physical parameters are analyzed and excited state energy consumption process is studied. Strong electrophilicity on acceptor is determined and the strength of nucleophilic sites on the bridge-phenyl of 2DQAO-bICz, 2QAO-bICz, 2SQAO-bICz and 2OQAO-bICz is increased, this promotes the short-range charge transfer property. In addition, the excitation processes for all studied molecules are dominated by long-range charge transfer from donor to acceptors, and supplemented by the short-range charge transfer on the bridge-phenyl with MR effect. Compromise energy gap and oscillator strength as well as large spin orbit coupling (SOC) constant are obtained for designed molecules. Thus, by regulating the long-range and short-range charge transfer ratios, excited state properties are successfully modulated and new efficient TADF molecules are proposed. Our research aims to provide deeper insight into long-range and short-range charge transfer features in balancing small ΔEST and large f, which could facilitate the development of novel efficient TADF molecules.

Modulation of Delayed Fluorescence Guided by Conformational Effect-Mediated Thermally Enhanced Phosphorescence in Phenothiazines-Quinoline-Cl Conjugates.

Triplet energy harvesting via thermally activated delayed fluorescence (TADF) from pure organic systems has attracted great attention in organic light-emitting diodes, sensing, and photocatalysis. However, the realization of thermally enhanced phosphorescence (TEP)-guided efficient TADF with a high rate of reverse intersystem crossing (kRISC) still needs to be discovered. Herein, we report two phenothiazine-quinoline conjugates (P2QC, P2QMC) comprising two phenothiazine donors covalently attached to the chlorine-substituted quinolinyl acceptor. Spectroscopic analysis in conjunction with quantum chemistry calculations reveals that TEP in P2QC originated due to slow internal conversion from higher-lying triplet to lowest triplet (T2' → T1') of the quasi-axial (QA) conformer and TADF (kRISC = 1.44 × 108 s-1) originated from the quasi-equatorial (QE) conformer caused by a low singlet-triplet gap (ΔES1-T1 = 0.11 eV) and triplet energy transfer from QA to QE owing to the degenerate ground state of the conformers. In contrast, TADF (kRISC = 0.74 × 108 s-1) and dual phosphorescence under ambient conditions are observed in P2QMC. This study provides a sustainable guideline for developing efficient TADF emitters via conformation effects and energy transfer mechanisms.

Enhanced Operational Stability by Cavity Control of Single-Layer Organic Light-Emitting Diodes Based on Thermally Activated Delayed Fluorescence.

Highly efficient organic light-emitting diodes (OLEDs) based on thermally activated delayed fluorescence (TADF) emitters have been realized in recent years, but the device lifetime needs further improvement for practical display or lighting applications. In this work, we present a device design principle by tuning the optical cavity of single-layer undoped devices, to realize efficient and long-lived TADF OLEDs. Extending the cavity length to the second-order interference maximum by increasing the emissive layer thickness broadens the recombination zone, while the optical outcoupling efficiency remains close to that of the thinner first-order devices. Such a device design leads to efficient and stable single-layer undoped OLEDs with a maximum EQE of 16%, a LT90 of 452h and LT50 of 3693h at an initial luminance of 1000cd m-2 , which is doubled compared to the first-order counterparts. We further demonstrate that the widely-used empirical relation between OLED lifetime and light-intensity originates from triplet-polaron annihilation, resulting in an extrapolated LT50 at 100cd m-2 of close to 90,000h, approaching the demands for practical backlight applications. This article is protected by copyright. All rights reserved.

Modulation of nonradiative emission decay rate by spacer unit in donor-acceptor TADF compounds

Highly emissive thermally activated delayed fluorescence (TADF) compounds typically are constructed from twisted donor and acceptor units, usually with the help of an additional spacer unit. Such molecular structure ensures low singlet-triplet energy gap, enabling the utilization of triplet states and boosting the emission yield. Here we show that emission yield also depends on the molecular structure of spacer unit. Selecting structurally flexible biphenyl spacer unit instead of rigid fluorene was shown to selectively enhance the nonradiative decay rate of triplet states (kNRT), leading to the lowered yield of delayed fluorescence (from 0.55 to 0.43). However, more rapid kNRT led in weaker OLED external quantum efficiency (EQE) roll-off due to lowered triplet lifetime, though at the cost of lower peak efficiency. The presented work highlights the need of careful design of spacer fragments for efficient TADF emitters.

Thiazoline Carbene−Au(I)−Amide complexes exhibiting dimer electroluminescence

Two-coordinate coinage metal (Cu, Ag and Au) complexes with linear carbene–metal–amide (CMA) structure have recently emerged as promising thermally activated delayed fluorescence (TADF) emitters for OLED application. Herein we investigate a series of eight new Au(I) CMA complexes, which incorporate derivatives of 1,3-thiazoline as N-heterocyclic carbene (NHC) ligands. The complexes exhibit blue to green luminescence in thin films. A limitation of the torsional motions around the metal-ligand axis in a combination with the heavy gold atom effect enables highly efficient TADF with photoluminescence quantum yield (PLQY) of up to 0.99 and radiative rates nearing 1·106 s−1. A formation of emissive dimers of complex molecules was observed in vacuum processed OLEDs. Achieved dual electroluminescence from the redshifted (by 120 nm) dimeric species in a combination with co-occurring monomer emission opens potential application prospects in construction of single-emitter white OLEDs.

Spiro Boron‐Nitrogen Molecules Based Thermally Activated Delayed Fluorescence Emitter for Highly Efficient Solution‐Processed Organic Light‐Emitting Diodes

AbstractSpiro compounds with unique structural and electronic properties are beneficial for thermally activated delayed fluorescence (TADF) emitters. Herein, a series of spiro boron‐nitrogen (B‐N) compounds are reported with donor–acceptor (D‐A) interaction through homoconjugation. Three phenyl acridine‐containing spiro B‐N compounds exhibit highly efficient photoluminescence (PL) in degassed toluene and solid‐state with obvious TADF character. The separation of HOMO and LUMO for these compounds is confirmed by theoretical calculations, as is the small ΔEST of phenyl acridine‐containing compounds. These three compounds are used as emitting layers in solution‐processed organic light‐emitting diodes (OLEDs), resulting in deep‐blue to green emission colors with different acceptor moieties. Impressively, an excellent external quantum efficiency (EQE) of 22.1% is recorded for the TPA‐s‐FMesBF‐based OLED device, which is comparable with the highest value from solution‐processed OLEDs based on spiro D‐A emitting materials. This work presents a facile synthetic route to novel B, N‐substituted spiro compounds, as well as the structure‐property relationship of spiro D‐A compounds for highly efficient TADF emitters.