Small Singlet-triplet Splitting Research Articles

Controlled Photooxidation via Singlet Oxygen Generation by Triplet Harvesting in a Heavy Atom Free Pure Organic Dithienylethene-Naphthalene Diimide.

Noninvasive control over the reversible generation of singlet oxygen (1O2) has found the enormous practical implications in the field of biomedical science. However, metal-free pure organic emitters, connected with a photoswitch, capable of generating "on-demand" 1O2 via triplet harvesting remain exceedingly rare; therefore, the utilization of these organic materials for the reversible control of singlet oxygen production remains at its infancy. Herein, an ambient triplet mediated emission in quinoline-dithienylethene (DTE)-core-substituted naphthalene diimide (cNDI) derivative is unveiled via delayed fluorescence. The quinoline-DTE-cNDI triad displayed enhanced photoswitching efficiency via double FRET mechanism. It was found to have direct utilization in controlled photosensitized organic transformations via efficient generation of singlet oxygen (yield ΦΔ~0.55 in DCM and 0.73 in methanol). The designed molecule exhibits a long-lived emission (τ∼1.1 μs) and very small singlet-triplet splitting (ΔEST) of 0.13 eV empowering it to display delayed fluorescence. Comprehensive steady state and time-resolved emission spectroscopy (TRES) analyses along with DFT calculations offer detailed understandings into the excited-state manifolds of organic compound and energy transfer (ET) pathways involved in 1O2 generation.

Ligand Characterization and DNA Intercalation of Ru(II) Polypyridyl Complexes: A Local Vibrational Mode Study.

We investigated in this work ruthenium-ligand bonding across the RuN framework in 12 Ru(II) polypyridyl complexes in the gas phase and solution for both singlet and triplet states, in addition to their affinity for DNA binding through π-π stacking interactions with DNA nucleobases. As a tool to assess the intrinsic strength of the ruthenium-ligand bonds, we determined local vibrational force constants via our local vibrational mode analysis software. We introduced a novel local force constant that directly accounts for the intrinsic strength of the π-π stacking interaction between DNA and the intercalated Ru(II) complex. According to our findings, [Ru(phen)2(dppz)]2+ and [Ru(phen)2(11-CN-dppz)]2+ provide an intriguing trade-off between photoinduced complex excitation and the strength of the subsequent π-π stacking interaction with DNA. [Ru(phen)2(dppz)]2+ displays a small singlet-triplet splitting and a strong π-π stacking interaction in its singlet state, suggesting a favorable photoexcitation but potentially weaker interaction with DNA in the excited state. Conversely, [Ru(phen)2(11-CN-dppz)]2+ exhibits a larger singlet-triplet splitting and a stronger π-π stacking interaction with DNA in its triplet state, indicating a less favorable photoinduced transition but a stronger interaction with DNA postexcitation. We hope our study will inspire future experimental and computational work aimed at the design of novel Ru-polypyridyl drug candidates and that our new quantitative measure of π-π stacking interactions in DNA will find a general application in the field.

High-performance fully solution-processed OLEDs based on carbazole-benzonitrile TADF emitter with long alkyl chains

The introduction of alkyl chains into the luminescent molecules will increase solubility and film-forming performance for fabricating solution-processed organic semiconductor devices. In this work, 5CzBN-9CSP and 5CzBN-12CSP with long alkyl chains were synthesized based on the typical thermally activated delayed fluorescence (TADF) molecule 5CzBN as core, and bipolar 9,9′-spirobi[fluorene] (SP) groups as peripheral dendrons. Not only the excellent solution processability is invested, but also the uniform photophysical property is sustained, including small singlet-triplet splitting energy (ΔEST) and high reverse intersystem crossing (RISC) rate. However, excessive length of alkyl chains degrading thermodynamic stability and carrier transport and balance, results in a maximum external quantum efficiency (EQEmax) of 17.6% for 5CzBN-12CSP-based fully solution-processed non-doped device, which is lower than that for 5CzBN-9CSP counterpart. Furthermore, TADF sensitized (TSF) solution-processed device obtains a high EQEmax of 25.9% within 5CzBN-12CSP host and multiple-resonance (MR) final emitter thanks to an efficient energy transfer.

Optical properties and exciton transfer between N-heterocyclic carbene iridium(III) complexes for blue light-emitting diode applications from first principles.

N-heterocyclic carbene (NHC) iridium(III) complexes are considered as promising candidates for blue emitters in organic light-emitting diodes. They can play the roles of the emitter as well as of electron and hole transporters in the same emission layer. We investigate optical transitions in such complexes with account of geometry and electronic structure changes upon excitation or charging and exciton transfer between the complexes from first principles. It is shown that excitation of NHC iridium complexes is accompanied by a large reorganization energy ∼0.7eV and a significant loss in the oscillator strength, which should lead to low exciton diffusion. Calculations with account of spin-orbit coupling reveal a small singlet-triplet splitting ∼0.1eV, whereas the oscillator strength for triplet excitations is found to be an order of magnitude smaller than for the singlet ones. The contributions of the Förster and Dexter mechanisms are analyzed via the explicit integration of transition densities. It is shown that for typical distances between emitter complexes in the emission layer, the contribution of the Dexter mechanism should be negligible compared to the Förster mechanism. At the same time, the ideal dipole approximation, although giving the correct order of the exciton coupling, fails to reproduce the result taking into account spatial distribution of the transition density. For charged NHC complexes, we find a number of optical transitions close to the emission peak of the blue emitter with high exciton transfer rates that can be responsible for exciton-polaron quenching. The nature of these transitions is analyzed.

Synthesis and photoinduced behavior of DPP-anchored nitronyl nitroxides: a multifaceted approach.

Understanding and controlling spin dynamics in organic dyes is of significant scientific and technological interest. The investigation of 2,5-dihydropyrrolo[4,3-c]pyrrolo-1,4-dione derivatives (DPPs), one of the most widely used dyes in many fields, has so far been limited to closed-shell molecules. We present a comprehensive joint experimental and computational study of DPP derivatives covalently linked to two nitronyl nitroxide radicals (DPPTh-NN2). Synthesis, single crystal X-ray diffraction study, photophysical properties, magnetic properties established using steady-state and pulse EPR, fast spin dynamics, and computational modelling using density functional theory and ab initio methods of electronic structure and spectroscopic properties of DPPTh-NN2 are presented. The single-crystal X-ray diffraction analysis of DPPTh-NN2 and computational modeling of its electronic structure suggest that effective conjugation along the backbone leads to noticeable spin-polarization transfer. Calculations using ab initio methods predict a weak exchange interaction of radical centers through a singlet ground state of DPPTh with a small singlet-triplet splitting (ΔEST) of about 25 cm-1 (∼0.07 kcal mol-1). In turn, a strong ferromagnetic exchange interaction between the triplet state of DPPTh chromophore and nitronyl nitroxides (with J ∼ 250 cm-1) was predicted.

Type I Photosensitization with Strong Hydroxyl Radical Generation in NIR Dye Boosted by Vigorous Intramolecular Motions for Synergistic Therapy.

Development of type I photosensitizers (PSs) with strong hydroxyl radical (·OH) formation is particularly important in the anaerobic tumor treatment. On the other hand, it is challenging to obtain an efficient solid-state intramolecular motion to promote the development of molecular machine and molecular motor. However, the relationship between them has never been revealed. In this work, we develop a pyrazine-based near-infrared type I PS with remarkable donor-acceptor effect. Notably, the intramolecular motions have almost been maximized by the combination of intramolecular and intermolecular engineering to simultaneously introduce the unlimited bond stretching vibration and boost the group rotation. The photothermal conversion caused by the intramolecular motions is realized with efficiency as high as 86.8%. The D-A conformation of PS can also induce a very small singlet-triplet splitting of 0.07eV, which is crucial to promote the intersystem crossing for the triplet sensitization. Interestingly, its photosensitization is closely related to the intramolecular motions, and a vigorous motion may give rise to a strong ·OH generation. In view of its excellent photosensitization and photothermal behavior, the biocompatible PS exhibits a superior imaging-guided cancer synergistic therapy. This work stimulates the development of advanced PS for the biomedical application and solid-state intramolecular motions. This article is protected by copyright. All rights reserved.

Synthesis and Properties of Short-Lifetime Thermally Activated Delayed Fluorescence Materials.

Compounds MBZ-mPXZ, MBZ-2PXZ, MBZ-oPXZ, EBZ-PXZ, and TBZ-PXZ were conveniently synthesized, and they were found to exhibit TADF properties with lifetimes of 857, 575, 561, 768, and 600 ns, respectively. These short lifetimes of the compounds might be due to the combination of small singlet-triplet splitting energy (ΔEST) and benzoate group, which could be an efficient strategy for the further design of short-lifetime TADF materials.

Recent Progress in Blue Thermally Activated Delayed Fluorescence Emitters and Their Applications in OLEDs: Beyond Pure Organic Molecules with Twist D-π-A Structures.

Thermally activated delayed fluorescence (TADF) materials, which can harvest all excitons and emit light without the use of noble metals, are an appealing class of functional materials emerging as next-generation organic electroluminescent materials. Triplet excitons can be upconverted to the singlet state with the aid of ambient thermal energy under the reverse inter-system crossing owing to the small singlet-triplet splitting energy (ΔEST). This results from a specific molecular design consisting of minimal overlap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital, due to the spatial separation of the electron-donating and electron-releasing part. When a well-designed device structure is applied, high-performance blue-emitting TADF organic light-emitting diodes can be realized with an appropriate molecular design. Unlike the previous literature that has reviewed general blue-emitting TADF materials, in this paper, we focus on materials other than pure organic molecules with twist D-π-A structures, including multi-resonance TADF, through-space charge transfer TADF, and metal-TADF materials. Cutting-edge molecules with extremely small and even negative ΔEST values are also introduced as candidates for next-generation TADF materials. In addition, OLED structures used to exploit the merits of the abovementioned TADF emitters are also described in this review.

Molecular engineering of blue diphenylsulfone-based emitter with aggregation-enhanced emission and thermally activated delayed fluorescence characteristics: impairing intermolecular electron-exchange interactions using steric hindrance

Thermally activated delayed fluorescence (TADF) emitters with aggregation-enhanced emission (AEE) characteristics are in high demand in organic light-emitting diodes (OLEDs) because of their strong fluorescence and high exciton utilization under electrical excitation. In this work, an AEE-active TADF emitter, 10,10′-(5-((9-phenyl-9H-carbazol-3-yl)sulfonyl)-1,3-phenylene)bis(9,9-dimethyl-9,10-dihydroacridine) (CZ-DPS-BAD), adopting diphenylsulfone skeleton as electron-accepting segment and 9-phenylcarbazole and 9,9-dimethyl-9,10-dihydroacridine as electron donors is developed. The small singlet-triplet splitting (0.13 eV) and high photoluminescence quantum yield (82 %) of CZ-DPS-BAD can attribute to the formation of large dihedral angles between electron donor-acceptors and weak electron-exchange interaction that suppress concentration quenching and exciton annihilation. The assigned characteristics result in reverse intersystem crossing rate of up to 5.0 × 105 s−1 and a delayed fluorescence lifetime of 5.3 μs. Notably, CZ-DPS-BAD behaves excellent non-doped OLED performance with the emission peak of 486 nm, the maximum current efficiency of 47.4 cd/A, the maximum power efficiency of 46.1 lm W−1, the maximum external quantum efficiency of 20.3 %, and the exciton utilizin efficiency of 83 %. It was also found that the short delayed fluorescence lifetime impair the triplet exciton annihilation resulting small efficiency roll-off in OLED. This work provides a general approach to explore new efficient and stable emitters by rationally regulating intermolecular interactions and integrating AEE and TADF, which facilitates their applications in optoelectronics.

Ornamenting of Blue Thermally Activated Delayed Fluorescence Emitters by Anchor Groups for the Minimization of Solid-State Solvation and Conformation Disorder Corollaries in Non-Doped and Doped Organic Light-Emitting Diodes.

Motivated to minimize the effects of solid-state solvation and conformation disorder on emission properties of donor–acceptor-type emitters, we developed five new asymmetric multiple donor–acceptor type derivatives of tert-butyl carbazole and trifluoromethyl benzene exploiting different electron-accepting anchoring groups. Using this design strategy, for a compound containing four di-tert-butyl carbazole units as donors as well as 5-methyl pyrimidine and trifluoromethyl acceptor moieties, small singlet-triplet splitting of ca. 0.03 eV, reverse intersystem crossing rate of 1 × 106 s–1, and high photoluminescence quantum yield of neat film of ca. 75% were achieved. This compound was also characterized by the high value of hole and electron mobilities of 8.9 × 10–4 and 5.8 × 10–4 cm2 V–1 s–1 at an electric field of 4.7 × 105 V/cm, showing relatively good hole/electron balance, respectively. Due to the lowest conformational disorder and solid-state solvation effects, this compound demonstrated very similar emission properties (emission colors) in non-doped and differently doped organic light-emitting diodes (OLEDs). The lowest conformational disorder was observed for the compound with the additional accepting moiety inducing steric hindrance, limiting donor–acceptor dihedral rotational freedom. It can be exploited in the multi-donor–acceptor approach, increasing the efficiency. Using an emitter exhibiting the minimized solid-state solvation and conformation disorder effects, the sky blue OLED with the emitting layer of this compound dispersed in host 1,3-bis(N-carbazolyl)benzene displayed an emission peak at 477 nm, high brightness over 39 000 cd/m2, and external quantum efficiency up to 15.9% along with a maximum current efficiency of 42.6 cd/A and a maximum power efficiency of 24.1 lm/W.

Exploiting new feasibility of a phenylquinoline unit for establishing efficient green thermally activated delayed fluorescent emitter with short delayed fluorescent lifetime

Realizing the confluence of high photoluminescence quantum yields (PLQYs) and short delayed fluorescent lifetimes remains a challenge for thermally activated delayed fluorescent (TADF) emitters. A green TADF emitter, 10-(2,4-diphenylquinolin-6-yl)-10 H -phenoxazine (PhQLPXZ), is exploited by directly linking an 2,4-diphenylquinoline unit with an electron-donating (D) 10 H -phenoxazine moiety. For the first time, the phenylquinoline (PhQL) unit is revealed as an electron-accepting unit for fabricating efficient TADF emitters. The dihedral angle between the donor and the acceptor is nearly 90°, which induces a totally separation of frontier orbitals. As a result, the emitter reveals a small singlet-triplet splitting energy of 0.09 eV and a short delayed fluorescence lifetime of 1.3 μs. The green organic light-emitting diodes (OLEDs) employing PhQLPXZ as the emitter exhibit a maximum external quantum efficiency of 15.7%. This study demonstrates for the first time that phenylquinoline derivatives can be employed for constructing TADF emitters for high-efficiency fluorescent OLEDs. • Phenylquinoline derivatives were employed to construct a green TADF emitter with a short delayed lifetime of 1.3 μs. • The molecule endows a vertical dihedral angle (97°) between the acceptor and the donor and high photoluminescence quantum yield over 70% in film. • The device with a doping concentration of 6% exhibited a high EQE of 15.7%, which is one of the best among the devices based on quinolone cored emitters.

Exciplex-Forming Systems of Physically Mixed and Covalently Bonded Benzoyl-1H-1,2,3-Triazole and Carbazole Moieties for Solution-Processed White OLEDs.

Using the newly designed exciplex-forming 1,2,3-triazole-based acceptors with fast and efficient singlet → triplet intersystem crossing (ISC) processes, carbazole and benzoyl-1H-1,2,3-triazole derivatives were synthesized by Dimroth-type 1,2,3-triazole ring formation and Ullmann–Goldberg C–N coupling reactions. Due to the exciplex formation between covalently bonded electron-donating (carbazole) and 1,2,3-triazole-based electron-accepting moieties with small singlet-triplet splitting (0.07–0.13 eV), the compounds exhibited ISC-assisted bluish–green thermally activated delayed fluorescence. The compounds were characterized by high triplet energy levels ranging from 2.93 to 2.98 eV. The most efficient exciplex-type thermally activated delayed fluorescence was observed for ortho-substituted carbazole-benzoyl-1H-1,2,3-triazole which was selected as a host in the structure of efficient solution-processed white light-emitting diodes. The best device exhibited a maximum power efficiency of 10.7 lm/W, current efficiency of 18.4 cd/A, and quantum efficiency of 7.1%. This device also showed the highest brightness exceeding 10 thousand cd/m2. Usage of the exciplex-forming host allowed us to achieve a low turn-on voltage of 3.6 V. High-quality white electroluminescence was obtained with the close to nature white color coordinates (0.31, 0.34) and a color rendering index of 92.

Bipolar 1,8-naphthalimides showing high electron mobility and red AIE-active TADF for OLED applications.

Aiming to design bipolar organic semiconductors with high electron mobility and efficient red thermally activated delayed fluorescence (TADF), three donor-acceptor compounds were designed and synthesized selecting 1,8-naphthalimide as an acceptor and phenoxazine, 3,7-di-tert-butylphenothiazine or 2,7-di-tert-butyldimethyl-9,10-dihydroacridine as donor moieties. Aggregation induced emission enhancement was detected for the compounds causing efficient TADF in the solid-state. Photoluminescence quantum yields up to 77% were observed for the films of the compounds doped in a host. The compounds exhibited small singlet-triplet splitting (0.03-0.05 eV), and high reverse intersystem crossing rates of 2.08 × 105-1.13 × 106 s-1. The compounds were characterized by satisfactory hole and electron-injecting properties with ionization potentials of 5.72-5.83 eV and electron affinities of 2.79-2.91 eV. Bipolar charge transport was revealed by time of flight measurements. Electron transport with low dispersity and mobilities exceeding 2 × 10-3 cm2 V-1 s-1 was observed at an electric field of 4.6 × 105 V cm-1. The compounds were used as emitters in red electroluminescent devices, which showed maximum external quantum efficiencies up to 8.2%. Utilization of host-guest systems as light-emitting materials with hosts preferably transporting holes and TADF guests which preferably transport electrons allowed maximum efficiencies to be achieved at a practical brightness of 700-2200 cd m-2. DFT calculations of the geometry, electronic structure, absorption and photoluminescence spectra of all compounds were carried out to prove the conclusions drawn from the experiment. The results of the calculations clearly show that the first excited state for all compounds is the intramolecular charge transfer state. Quantitative analysis of the separation degree of electronic density during excitation allows the observed dependence of the blue shift value in the absorption and emission spectra on the increasing polarity of the solvent to be explained.

Construction of High-Performance Carbene–Metal–Amide-Like TADF Materials: A Theoretical Study

Thermally activated delayed fluorescence (TADF) molecules based on carbene–metal–amides (CMAs) have attracted tremendous attention, but it remains a great challenge for the rational design of such materials due to the lack of reliable molecular construction guidelines. In this work, we perform a computational investigation to design CMA-based TADF materials by elucidating how the location (α, β) and number of nitrogen atoms in carbolines affect the TADF properties. Four promising CMA-based TADF molecules with both small splitting energy and large fluorescence oscillator strength were successfully designed. Moreover, it was found that β-position with one and two N atoms are promising in achieving improved TADF performance in light of their small geometric relaxations, low energy barriers for electron injection, small singlet–triplet splitting energies, facile intersystem crossing, and efficient fluorescence radiative rates. These theoretical understandings could give an in-depth physical insight into the structure–performance relationship of CMA-based luminescent materials, providing important guidance for the exploration of high-performance TADF molecules.

Chiral thermally activated delayed fluorescence emitters for circularly polarized luminescence and efficient deep blue OLEDs

The development of the thermally activated delayed fluorescence (TADF) emitters with circularly polarized luminescence (CPL), particularly those exhibiting deep-blue emission is still a formidable challenge. In this work, we reported a simple and easily accessed molecular design strategy for deep-blue circularly polarized TADF (CP-TADF) enantiomers. Two chiral compounds, namely (S)-NPE-AcDPS and (R)-NPE-AcDPS, were successfully designed and synthesized, which featured concurrently TADF, CPL, and aggregation-induced enhanced emission (AIEE) properties. The CPL exhibited a maximum gPL value of 3.0 × 10−4. These emitters exhibited deep blue emission peaking at 451 nm in doped film with a high photoluminescence of 86% and a small singlet-triplet splitting of 0.05 eV. Furthermore, the deep blue OLED based on (S)-NPE-AcDPS demonstrated a high external quantum efficiency (EQE) up to 18.5%.

Spiro-Based Thermally Activated Delayed Fluorescence Emitters with Reduced Nonradiative Decay for High-Quantum-Efficiency, Low-Roll-Off, Organic Light-Emitting Diodes.

Herein, we report the use of spiro-configured fluorene-xanthene scaffolds as a novel, promising, and effective strategy in thermally activated delayed fluorescence (TADF) emitter design to attain high photoluminescence quantum yields (ΦPL), short delayed luminescence lifetime, high external quantum efficiency (EQE), and minimum efficiency roll-off characteristics in organic light-emitting diodes (OLEDs). The optoelectronic and electroluminescence properties of SFX (spiro-(fluorene-9,9'-xanthene))-based emitters (SFX-PO-DPA, SFX-PO-DPA-Me, and SFX-PO-DPA-OMe) were investigated both theoretically and experimentally. All three emitters exhibited sky blue to green emission enabled by a Herzberg-Teller mechanism in the excited state. They possess short excited-state delayed lifetimes (<10 μs), high photoluminescence quantum yields (ΦPL ∼ 70%), and small singlet-triplet splitting energies (ΔEST < 0.10 eV) in the doped films in an mCP host matrix. The OLEDs showed some of the highest EQEs using spiro-containing emitters where maximum external quantum efficiencies (EQEmax) of 11 and 16% were obtained for devices using SFX-PO-DPA and SFX-PO-DPA-OMe, respectively. Further, a record EQEmax of 23% for a spiro-based emitter coupled with a low efficiency roll-off (19% at 100 cd m-2) was attained with SFX-PO-DPA-Me.

Efficient Intramolecular Charge-Transfer Fluorophores Based on Substituted Triphenylphosphine Donors.

Triphenylphosphine (TPP)-based luminescent compounds are rarely investigated because of the low photoluminescence quantum yield (PLQY). Here, we demonstrate that introducing steric hindrance groups to the TPP moiety and separating the orbitals involved in the transition can drastically suppress the non-radiative decay induced by structural distortion of TPP in the excited state. High PLQY up to 0.89 as well as thermally activated delayed fluorescence are observed from the intramolecular charge-transfer (ICT) molecules with substituted TPP donors (sTPPs) in doped films. The red organic light-emitting diodes employing these emitters achieve comparable external quantum efficiencies to the control device containing a classical phosphorescent dye, revealing the great potential of the ICT emitters based on electrochemically stable sTPPs.

Spatial donor/acceptor architecture for intramolecular charge-transfer emitter

Charge transfer via electron hopping from an electron donor (D) to an acceptor (A) in nanoscale, plays a crucial role in optoelectronic materials, such as organic light-emitting diodes (OLEDs) and organic photovoltaic cells (OPVs). Here, we propose a strategy for binding D/A units in space, where intramolecular charge-transfer can take place. The resulted material DM-Me-B is able to give bright emission in this molecular architecture because of the good control of D/A interaction and conformational rigidity. Moreover, DM-Me-B presents small singlet-triplet splitting energy, enabling thermally activated delayed fluorescence. Therefore, the DM-Me-B exhibits ∼20% maximum external quantum efficiency and low efficiency roll-off at 1000 cd/m2, certifying an effective strategy in controlling D/A blocks through space.

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(10H-phenoxazine) (Fene), 10,10'-(quinoline-2,8-diyl)bis(10H-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 excellent maximum external quantum efficiencies (EQEmax) 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 to 3.2 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.

Asymmetric Thermally Activated Delayed Fluorescence Materials With Aggregation-Induced Emission for High-Efficiency Organic Light-Emitting Diodes.

The exploitation of thermally activated delayed fluorescence (TADF) emitters with aggregation-induced emission is highly prerequisite for the construction of highly efficient electroluminescent devices in materials science. Herein, two asymmetric TADF emitters of SFCOCz and SFCODPAC with charming aggregation-induced emission are expediently designed and prepared based on highly twisted strong electron-withdrawing acceptor (A) of sulfurafluorene (SF)-modified ketone (CO) and arylamine donor (D) in D1−A–D2 architecture by simple synthetic procedure in high yields. High photoluminescence quantum yields up to 73% and small singlet–triplet splitting of 0.03 eV; short exciton lifetimes are obtained in the resultant molecules. Strikingly, efficient non-doped and doped TADF organic light-emitting diodes (OLEDs) facilitated by these emitters show high luminance of 5,598 and 11,595 cd m−2, current efficiencies (CEs) of 16.8 and 35.6 cd/A, power efficiencies (PEs) of 9.1 and 29.8 lm/W, and external quantum efficiencies (EQEs) of 7.5 and 15.9%, respectively. This work furnishes a concrete instance in exploring efficient TADF emitter, which is highly conducive and encouraging in stimulating the development of TADF OLEDs with high brightness and excellent efficiencies simultaneously.