Language：English   Publisher：Nature Communications  

In recent years, thermally activated delayed fluorescence (TADF) has attracted intense attention owing to its straightforward application to high-efficiency organic light-emitting diodes. Further, to develop high-performance TADF materials, many researchers have designed novel molecules that have a small energy gap between the lowest excited singlet and triplet states (ΔEST), and detailed analysis suggests a significant contribution of higher-lying excited states for spin flipping processes. In this study, we demonstrate a peculiar thermal behaviour of emission decay of a donor–acceptor type TADF molecule, TMCz-BO, which seems like thermal deactivation of delayed fluorescence that can be explained without a negative ΔEST by comprehensive kinetic analysis across various temperatures and solvents. While the activation energy has previously been treated as being temperature-independent, we stress that it should be a dynamic parameter affected by changing the solvent-solute interaction with the environmental temperature, especially in the case of a small energy gap.

DOI： 10.1038/s41467-025-59910-z

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Publisher：Advanced Optical Materials  

Multiple-resonance (MR) type emitters have overcome several issues in organic light-emitting diodes (OLEDs) because of their narrowband emission and high electroluminescence quantum yield efficiency. Also, this kind of emitters has been widely used as hyperfluorescence (HF)-OLEDs thanks to their advantageous properties. However, there has been a significant challenge for HF-OLEDs based on MR emitters, which is impacted by the nature of the long-lived triplet excitons of MR emitters, as there is a trade-off between narrowband emission and short exciton lifetime. Herein, the low-possessed triplet energy level of pyrene is introduced to an MR core unit to achieve stable HF-OLEDs with the development of three isomers to investigate the regioisomer effect of pyrenes. The improved device lifetimes are successfully achieved, and the reasons for the differences in excimer formation and stability between those three isomers are studied.

DOI： 10.1002/adom.202402862

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Language：English   Publisher：Angewandte Chemie International Edition  

The pursuit of highly efficient thermally activated delayed fluorescence (TADF) emitters with two-photon absorption (2PA) character is hampered by the concurrent achievement of a small singlet-triplet energy gap (ΔE<inf>ST</inf>) and high photoluminescence quantum yield (Φ<inf>PL</inf>). Here, by introducing a terephthalonitrile unit into a sterically crowded donor-π-donor structure, inducing a hybrid electronic excitation character, we designed unique TADF emitters possessing 2PA ability. This rational molecular design was achieved through a main π-conjugated donor-acceptor-donor backbone in line with locally excited feature renders a large oscillator strength and transition dipole moment, maintaining a high 2PA cross-section value. The ancillary N-donor-acceptor-donor with charge transfer character highly balances the TADF phenomenon by minimizing ΔE<inf>ST</inf>. A near-unity Φ<inf>PL</inf> value with a large radiative decay rate over an order of magnitude higher than the intersystem crossing rate and a high horizontal orientation ratio of 0.95 were simultaneously attained for TPCz2NP. The organic light-emitting diodes fabricated with this material exhibit a high maximum external quantum efficiency of 25.4 % with an elevated 2PA cross-section (σ<inf>2</inf>) value up to 143 GM at 850 nm. These findings offer a venue for designing high-performance TADF emitters with exceptional performance inclusive of 2PA properties, expanding for future functional material design.

DOI： 10.1002/anie.202420417

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PubMed

Publisher：Chemical Physics Letters  

We investigate the photophysical properties of a newly synthesized molecule, 2PhCz-3PhTrz-DMeCz, which has two phenyl carbazole (PhCz) donors and a triphenyl triazine (3PhTrz) acceptor connected by a dimethyl carbazole (DMeCz) spacer. This architecture enables both through-bond charge-transfer (TBCT) and through-space CT (TSCT) interactions. In polar solvents, the molecule exhibits enhanced photoluminescence quantum yield (PLQY) and reverse intersystem crossing rate (k<inf>RISC</inf>). Theoretical calculations show that polar solvents reduce the dihedral angle between PhCz and DMeCz in the excited states, increasing hole delocalization across the molecule. Our finding highlights that the conformational change of the target molecule is strongly influenced by the solvent polarity, resulting in distinct photophysical behavior.

DOI： 10.1016/j.cplett.2024.141835

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Language：English   Publisher：Angewandte Chemie International Edition  

Photon-upconversion (PUC) processes in organic molecular systems, such as triplet-triplet upconversion and hot-band absorption, are promising technologies for future energy harvesting. Although these processes can generate high-energy excitons compared to excitation energy, a PUC process with a high yield and no energy loss has not been established and, therefore, is highly desired. Here, we propose an alternative PUC mechanism that uses reverse intersystem crossing on thermally activated delayed fluorescence (TADF) molecules. This process combines a triplet sensitizer and a TADF molecule, generating a triplet in the former and transferring it to the latter. Specifically, the triplet energy transfer from Ir(ppy)<inf>3</inf> (sensitizer) to CzBSe (TADF) results in anti-Stokes emission with an anti-Stokes energy of 0.18 eV. We found that the triplet energy transfer rate strongly depends on the triplet radiative decay rate of TADF molecules and the difference in Gibbs energy between the energy acceptor and donor. Our findings will contribute to understanding triplet energy transfer dynamics in organic energy donor-acceptor systems and will lead to various applications, such as future optical cooling systems.

DOI： 10.1002/anie.202419323

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Language：English   Publisher：Nature Communications  

The attainment of white emission from a light-emitting electrochemical cell (LEC) is important, since it enables illumination and facile color conversion from devices that can be cost-efficient and sustainable. However, a drawback with current white LECs is that they either employ non-sustainable metals as an emitter constituent or are intrinsically efficiency limited by that the emitter only converts singlet excitons to photons. Organic compounds that emit by thermally activated delayed fluorescence (TADF) can address these issues since they can harvest all excitons for light emission while being metal free. Here, we report on the first white LEC based on solely metal-free TADF emitters, as accomplished through careful tuning of the energy-transfer processes and the electrochemically formed doping structure in the single-layer active material. The designed TADF-LEC emits angle-invariant white light (color rendering index = 88) with an external quantum efficiency of 2.1 % at a luminance of 350 cd/m².

DOI： 10.1038/s41467-025-55954-3

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PubMed

Publisher：Advanced Functional Materials  

While metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) have been widely investigated as porous conductive materials, the research on the electrical properties of HOF materials has been limited. Moreover, the electrical conductivity of HOF materials is typically several orders of magnitude lower than that of MOFs and COFs. In this work, a HOF material based on naphthalene diimide is designed and achieved a remarkable electrical conductivity of 2.9 × 10⁻² S cm⁻¹ after hydrazine doping, which represents the highest value reported in the HOF system to date. In addition, this material exhibits a reversible change of its electrical conductivity under exposure to ammonia which is promising for gas-sensor applications. The demonstration reveals a new dimension of HOFs as conductive materials and opens up possibilities for new HOF-based devices.

DOI： 10.1002/adfm.202409299

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Language：English   Publisher：Physical Chemistry Chemical Physics  

Two novel deep-blue multi-resonance thermally activated delayed fluorescence (MR-TADF) emitters, 1B-CzCrs and 2B-CzCrs, containing a fused carbazole unit were synthesized. The carbazole contributed to the emergence of TADF in these small molecules. Particularly, organic light-emitting diodes with 1B-CzCrs doped in the mCP host achieve a maximum external quantum efficiency of 12.8% at CIE coordinates of (0.146, 0.062).

DOI： 10.1039/d4cp02664k

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Language：English   Publisher：ACS Nano  

The spatial distribution and electronic properties of the frontier molecular orbitals (FMOs) in a thermally activated delayed fluorescence (TADF) molecule contribute significantly to the TADF properties, and thus, a detailed understanding and sophisticated control of the FMOs are fundamental to the design of TADF molecules. However, for multiple-resonance (MR)-TADF molecules that achieve spatial separation of FMOs by the MR effect, the distinctive distribution of these molecular orbitals poses significant challenges for conventional computational analysis and ensemble averaging methods to elucidate the FMOs’ separation and the precise mechanism of luminescence. Therefore, the visualization and analysis of electronic states with the specific energy level of a single MR-TADF molecule will provide a deeper understanding of the TADF mechanism. Here, scanning tunneling microscopy/spectroscopy (STM/STS) was used to investigate the electronic states of the DABNA-1 molecule at the atomic scale. FMOs’ visualization and local density of states analysis of the DABNA-1 molecule clearly show that MR-TADF molecules also have well-separated FMOs according to the internal heteroatom arrangement, providing insights that complement existing theoretical prediction methods.

DOI： 10.1021/acsnano.4c04813

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Language：English   Publisher：Advanced Materials  

Narrowband emissive multiresonant thermally activated delayed fluorescence (MR-TADF) emitters are a promising solution to achieve the current industry-targeted color standard, Rec. BT.2020-2, for blue color without using optical filters, aiming for high-efficiency organic light-emitting diodes (OLEDs). However, their long triplet lifetimes, largely affected by their slow reverse intersystem crossing rates, adversely affect device stability. In this study, a helical MR-TADF emitter (f-DOABNA) is designed and synthesized. Owing to its π-delocalized structure, f-DOABNA possesses a small singlet-triplet gap, ΔE<inf>ST</inf>, and displays simultaneously an exceptionally faster reverse intersystem crossing rate constant, k<inf>RISC</inf>, of up to 2 × 10⁶ s⁻¹ and a very high photoluminescence quantum yield, Φ<inf>PL</inf>, of over 90% in both solution and doped films. The OLED with f-DOABNA as the emitter achieved a narrow deep-blue emission at 445 nm (full width at half-maximum of 24 nm) associated with Commission Internationale de l'Éclairage (CIE) coordinates of (0.150, 0.041), and showed a high maximum external quantum efficiency, EQE<inf>max</inf>, of ≈20%.

DOI： 10.1002/adma.202402289

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Publisher：Advanced Optical Materials  

Although thermally activated delayed fluorescence (TADF) based organic light-emitting diodes (OLEDs) continue to achieve high efficiencies, their device stability still does not necessarily meet industrial standards. To improve device stability, careful design of a stable host material is crucial. Herein, with reference to a common p-type host material, 3,3′-di(9H-carbazol-9-yl)-1,1′-biphenyl (mCBP), three novel host materials based on a pyridine unit, mCBP-1N, CzPyPhCz, and CzPyBF, are systematically designed to improve the stabilities efficiently. The green and blue TADF OLEDs are fabricated with these three new hosts. The maximum external quantum efficiencies (EQE<inf>max</inf>s) of green OLEDs are 20.3 % and 14.0% for CzPyBF and mCBP hosts, respectively. Further, high EQEs of 19.2% and 12.9% are maintained even at 1000 cd m⁻². Most importantly, the device lifetime of the CzPyBF host can achieve LT<inf>95</inf> of 62.7 h, which is 2.5 times longer than that of mCBP. Also, lower turn-on voltages are achieved by using CzPyPhCz in blue and green devices. With host engineering, the TADF OLEDs are simultaneously improved with lower turn-on voltages, higher EQEs, and longer device lifetimes.

DOI： 10.1002/adom.202302971

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Language：English   Publisher：Nature Communications  

To fulfill ultra-high-definition display, efficient and bright green organic light-emitting diodes with Commission Internationale de l’Éclairage y-coordinate ≥ 0.7 are required. Although there are some preceding reports of highly efficient devices based on pure-green multi-resonance emitters, the efficiency rolloff and device stabilities for those pure-green devices are still unsatisfactory. Herein, we report the rational design of two pure-green multi-resonance emitters for achieving highly stable and efficient pure-green devices with CIE<inf>x,y</inf>s that are close to the NTSC and BT. 2020 standards. In this study, our thermally activated delayed fluorescence OLEDs based on two pure-green multi-resonance emitters result in CIE<inf>y</inf> up to 0.74. In hyperfluorescent device architecture, the CIE<inf>x</inf>s further meet the x-coordinate requirements, i.e., NTSC (0.21) and BT. 2020 (0.17), while keeping their CIE<inf>y</inf>s ~ 0.7. Most importantly, hyperfluorescent devices display the high maximum external quantum efficiencies of over 25% and maximum luminance of over 10⁵ cd m⁻² with suppressed rolloffs (external quantum efficiency of ~20% at 10⁴ cd m⁻²) and long device stabilities with LT<inf>95</inf>s of ~ 600 h.

DOI： 10.1038/s41467-024-47482-3

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Publisher：Chemistry Letters  

In recent decades, various types of aryl-substituted 1,3,5-triazine derivatives have been applied in many research fields, including biomedical chemistry, non-linear optics, and organic electronics. However, the substituent scope for 4,6-diaryl-1,3,5-triazines (DAr-TRZs) remains limited. Here, we present our work on the synthesis of 2-amino- and 2-bromo-DAr-TRZ derivatives bearing electron-withdrawing groups on the aryl rings. Our synthetic methods successfully provided trifluoromethyl-, nitrile-, and nitro-substituted DAr-TRZs. These will expand the structural diversity of conventional triazine-based functional materials.

DOI： 10.1093/chemle/upae059

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Language：English   Publisher：Faraday Discussions  

In recent years, much attention has been paid to the development of thermally activated delayed fluorescence (TADF) materials with short delayed-fluorescence lifetimes to improve the device performances of OLEDs. In principle, by reducing the highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) overlap, while the energy difference between S<inf>1</inf>-T<inf>1</inf> (ΔE<inf>ST</inf>) and activation energy (E<inf>a</inf>) can be reduced, and the reverse intersystem crossing rate constant (k<inf>RISC</inf>) can be accelerated, a decrease in the radiative rate constant happens, necessitating an advanced molecular design. Furthermore, a molecule based on heptazine as a parent skeleton has recently been found to have a peculiar temperature dependence of luminescence decay, suggesting a negative gap (NG) material. In this report, we show that 9-[1,4]benzoxaborino[2,3,4-kl]phenoxaborine-7-yl-1,3,6,8-tetramethyl-9H-carbazole (TMCz-BO), a donor-acceptor linked TADF molecule with a very short delay lifetime of 750 ns, exhibits a peculiar thermal behavior similar to that of NG materials based on the temperature dependence of its luminescence decay in solution.

DOI： 10.1039/d3fd00151b

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Language：English   Publisher：Angewandte Chemie International Edition  

Photon-upconversion in organic molecular systems is one of the promising technologies for future energy harvesting systems because these systems can generate excitons that possess higher energy than excitation energy. The photon-upconversion caused by absorbing ambient heat as additional energy is particularly interesting because it could ideally provide a light-driving cooling system. However, only a few organic molecular systems have been reported. Here, we report the anti-Stokes photoluminescence (ASPL) derived from hot-band absorption in a series of multi-resonance-type thermally-activated delayed fluorescence (MR-TADF) molecules. The MR-TADF molecules exhibited an anti-Stokes shift of approximately 0.1 eV with a high PL quantum yield in the solution state. The anti-Stokes shift corresponded well to the 1–0 vibration transition from the ground state to the excited singlet state, and we further evaluated a correlation between the activation energy for the ASPL intensity and the TADF process. Our demonstration underlines that MR-TADF molecules have become a novel class of ASPL materials for various future applications, such as light-driving cooling systems.

DOI： 10.1002/anie.202312326

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Publisher：ACS Materials Letters  

Type II heterostructures formed by organic semiconducting ligands and inorganic layers in two-dimensional (2D) hybrid perovskites can offer separated charge transport channels for holes and electrons. In this work, we studied a new lead-based 2D Dion-Jacobson perovskite structure incorporating simple terphenyl diammonium salts as organic spacers. The investigations of the electronic and photophysical properties, combined with theoretical calculations, indicate that this 2D perovskite structure forms a type II heterostructure producing intercalated separate pathways for electrons and holes that can migrate within the inorganic and organic sublayers, respectively. The charge transport properties of this unusual type II 2D perovskite heterostructure have also been successfully investigated for the first time by the space charge limited current (SCLC) method, and maximum electron and hole mobilities based on single-crystal devices were evaluated to be 0.3 cm² V^-1 s^-1 and 7.0 × 10^-4 cm² V^-1 s^-1, respectively. This work gives valuable insights into the charge transport mechanisms of type II heterostructures and paves the way toward optoelectronic device applications for such Dion-Jacobson-type 2D perovskites.

DOI： 10.1021/acsmaterialslett.3c00509

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Publisher：Journal of Materials Chemistry C  

Two novel π-extended amine/carbonyl-based multi-resonance thermally activated delayed fluorescence (MR-TADF) emitters have been designed and synthesized. The two emitters are isomeric, composed of nine fused rings and show green-yellow emission. Sym-DiDiKTa and Asym-DiDiKTa possess tert-butyl groups distributed in a symmetrical and asymmetrical fashion, respectively, which significantly impact the single-crystal packing structure. The two compounds possess similar singlet-triplet energy gaps, ΔE<inf>ST</inf>, of around 0.23 eV, narrowband emission characterized by a full-width at half-maximum, FWHM, of 29 nm and a photoluminescence quantum yield, Φ<inf>PL</inf>, of 70% and 53% for the symmetric and asymmetric counterparts, respectively, in toluene. Investigation in OLEDs demonstrated that the devices with Sym-DiDiKTa and Asym-DiDiKTa displayed electroluminescence maxima of 543 and 544 nm, and maximum external quantum efficiencies (EQE<inf>max</inf>) of 9.8% and 10.5%, respectively. The maximum EQE was further improved to 19.9% by employing a hyperfluorescence strategy. We further present the first example of a neutral MR-TADF emitter incorporated in a LEC device where Sym-DiDiKTa acts as the emitter. The LEC shows a λ<inf>EL</inf> at 551 nm and FWHM of 60 nm with luminance of 300 cd m⁻² and a fast turn-on time of less than 2 s to 100 cd m⁻²

DOI： 10.1039/d3tc00641g

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Language：Japanese   Publisher：The Japanese Photochemistry Association  

<p>For the development of thermally activated delayed fluorescence (TADF) materials, the kinetic analysis is crucial to estimate the rate constants of each photophysical process. Until now, however, a wide variety of rate equations has been formulated with different assumptions. Since most of the rate equations are assuming non-radiative decay from singlet or triplet as zero, they cannot apply to low emissive materials. Also, the conventional estimation method for prompt and delayed emission efficiency should be corrected. In this report, we formulated the accurate kinetic rate equations to analyze the three-state photophysics. Further, we provided the accurate analysis method to evaluate the effective spin-orbit coupling strength from the temperature dependence of the rate constants. We believe that these advanced photophysical parameters provide the design rule for high performance TADF materials.</p>

DOI： 10.60391/koukagaku.54.1_28

CiNii Research

Publisher：Chemistryselect  

Three new 1,2,4,5-tetraphenylimidazole derivatives, 9,9-dimethyl-10-(4-(2,4,5-triphenyl-1H-imidazol-1-yl)phenyl)-9,10-dihydroacridine (DMAC-TPI), 10-(4-(2,4,5-triphenyl-1H-imidazol-1-yl)phenyl)-10H-phenoxazine (PXZ-TPI), and 10-(4-(2,4,5-triphenyl-1H-imidazol-1-yl)phenyl)-10H-phenothiazine (PTZ-TPI), bearing different electron donors at the N1 position of the imidazole were synthesised and characterised. DMAC-TPI and PXZ-TPI showed narrow emission at λ<inf>PL</inf> of 388 and 418 nm in toluene, and in doped films in Zeonex polymer (1 wt.%) at λ<inf>PL</inf> 381 and 407 nm, respectively, with a full width at half maximum (FWHM) ranging 0.42-0.44 eV. DMAC-TPI and PXZ-TPI are predicted to show very low oscillator strength for the low-energy transitions, which aligns to the observed low photoluminescence quantum yields. Both molecules showed a singlet-triplet energy gap (ΔE<inf>ST</inf> of around 1.2 eV) that is much too large to enable reverse intersystem crossing and thermally activated delayed fluorescence. Connecting a donor group to TPI at the N1 position can lead to room temperature phosphorescence (RTP), as the example of PTZ-TPI showed.

DOI： 10.1002/slct.202300274

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Language：English   Publisher：Angewandte Chemie International Edition  

While materials based on organic molecules usually have either superior optoelectronic or superior chiral properties, the combination of both is scarce. Here, a crystalline chiroptical film based on porphyrin with homochiral side groups is presented. While the dissolved molecule has a planar, thus, achiral porphyrin core, upon assembly in a metal–organic framework (MOF) film, the porphyrin core is twisted and chiral. The close packing and the crystalline order of the porphyrin cores in the MOF film also results in excellent optoelectronic properties. By exciting the Soret band of porphyrin, efficient photoconduction with a high On-Off-ratio is realized. More important, handedness-dependent circularly-polarized-light photoconduction with a dissymmetry factor g of 4.3×10⁻⁴ is obtained. We foresee the combination of such assembly-induced chirality with the rich porphyrin chemistry will enable a plethora of organic materials with exceptional chiral and optoelectronic properties.

DOI： 10.1002/anie.202217377

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Language：English   Publisher：Journal of the American Chemical Society  

Multiple-resonance thermally activated delayed fluorescence (MR-TADF) emitters have emerged as an important component of organic light-emitting diodes (OLEDs) because of their narrowband emission and high exciton utilization efficiency. However, the chemical space of MR-TADF emitters remains mostly unexplored because of the lack of suitable synthetic protocols. Herein, we demonstrate a sequential multiple borylation reaction that provides new synthetically accessible chemical space. ω-DABNA, the proof-of-concept material, exhibited narrowband green TADF with a full width at half-maximum of 22 nm and a small singlet-triplet energy gap of 13 meV. The OLED employing it as an emitter exhibited electroluminescence at 512 nm, with Commission International de l’Éclairage coordinates of (0.13, 0.73) and a high external quantum efficiency (EQE) of 31.1%. Moreover, the device showed minimum efficiency roll-off, with an EQE of 29.4% at 1000 cd m^-2

DOI： 10.1021/jacs.2c10946

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Publisher：Chemical Physics Letters  

The solvent effects were studied on charge-transfer excited states in a donor–acceptor-type luminescent material, phenothiazine-triphenyltriazine, which has two distinct conformers: quasi-coplanar and perpendicular conformers. The solvent dielectric permittivity dependence of the steady-state photoluminescence spectra using solvent mixtures of toluene and tetrahydrofuran (THF) indicated that the two conformers have nearly identical excited-state dipole moments. The time-resolved photoluminescence and transient absorption spectra in toluene and THF showed different solvent dependences for the two conformers. A detailed analysis of these time-resolved spectra revealed solvent-dependent emission processes in the two conformers.

DOI： 10.1016/j.cplett.2022.140155

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Language：English   Publisher：Chemical Communications  

For a long period of time, while the glass transition temperature (T<inf>g</inf>) had been mainly focused on in polymer science, the T<inf>g</inf> values of small organic materials have been recognized to be important not only in medicines but also in a wide variety of organic optoelectronics in recent years. In this study, we report a useful and convenient “melt-blending” method to estimate organic semiconductor materials’ T<inf>g</inf> values, which are hard to observe when each material exists independently. We revealed that some cases reported incorrect T<inf>g</inf> values.

DOI： 10.1039/d2cc01467j

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PubMed

Publisher：Advanced Functional Materials  

Light-emitting electrochemical cells (LECs) comprising metal-free molecules that emit by the process of thermally activated delayed fluorescence (TADF) can be both sustainable and low cost. However, the blue emission performance of current TADF-LECs is unfortunately poor, which effectively prohibits their utilization in important applications, such as illumination and full-color displays. Here, this drawback is addressed through the development of a TADF-LEC, which delivers blue light emission (peak wavelength = 475 nm) with a high external quantum efficiency of 5.0%, corresponding to a current efficacy of 9.6 cd A^-1. It is notable that this high efficiency is attained at bright luminance of 740 cd m^-2, and that the device turn-on is very fast. It is demonstrated that this accomplishment is enabled by the blending of a carbazole-based 9-(4-(4,6-diphenyl-1,3,5-triazin-2-yl)-2-methylphenyl)-3,6-dimethyl-9H-carbazole guest emitter with a compatible carbazole-based tris(4-carbazoyl-9-ylphenyl)amine:2,6-bis(3-(carbazol-9-yl)phenyl)pyridine blend-host for the attainment of bipolar electrochemical doping, balanced electron/hole transport, and exciplex-effectuated host-to-guest energy transfer.

DOI： 10.1002/adfm.202205967

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Language：English   Publisher：Frontiers in Chemistry  

We studied the photophysical and electroluminescent (EL) characteristics of a series of azaborine derivatives having a pair of boron and nitrogen aimed at the multi-resonance (MR) effect. The computational study with the STEOM-DLPNO-CCSD method clarified that the combination of a BN ring-fusion and a terminal carbazole enhanced the MR effect and spin-orbit coupling matrix element (SOCME), simultaneously. Also, we clarified that the second triplet excited state (T<inf>2</inf>) plays an important role in efficient MR-based thermally activated delayed fluorescence (TADF). Furthermore, we obtained a blue–violet OLED with an external EL quantum efficiency (EQE) of 9.1%, implying the presence of a pronounced nonradiative decay path from the lowest triplet excited state (T<inf>1</inf>).

DOI： 10.3389/fchem.2022.990918

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PubMed

Publisher：Advanced Optical Materials  

Multi-resonance emitters (MREs) are a promising candidate for fulfilling the harsh requirements of display applications due to their unique photophysical properties. Recently, MREs have been widely used as a terminal emitter in hyperfluorescence organic light-emitting diodes (HF-OLEDs); however, since MREs are always thermally activated delayed fluorescence (TADF)-active, possessing long triplet lifetimes in millisecond order, they result in severe chemical degradation. Instead of shortening the delayed lifetime of MREs by molecular design, herein, a low-triplet pyrene unit is introduced into an MRE scaffold to achieve narrowband emission and quick removal of triplets in MREs simultaneously. Blue HF-OLED based on the non-TADF MRE demonstrates a high external quantum efficiency of 20% and a tenfold improvement in stability, compared to those of the HF-OLEDs with standard MREs. An opposite direction of molecular design of MREs for the sophisticated exciton generation and transfer system in HF-OLEDs is proposed to enhance device lifetime without sacrificing color purity and efficiency.

DOI： 10.1002/adom.202200682

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Language：English   Publisher：Chemical Science  

The solvent plays an important role in the photophysical properties of donor-acceptor based photocatalysts. The solvent-dependent access to E vs. Z-allylic amines was achieved via decarboxylative vinylation of amino acids with vinyl sulfones. Detailed experimental studies have been conducted to understand the role of the solvent in the reactivity and stereoselectivity of the vinylation reactions.

DOI： 10.1039/d2sc02090d

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PubMed

Language：English   Publisher：Chemical Communications  

Two new deep-blue narrowband multi-resonant emitters, 1B-DTACrs and 2B-DTACrs, one of which shows thermally activated delayed fluorescence (TADF), based on boron, nitrogen, and oxygen doped nanographenes are reported. Devices based on 2B-DTACrs showed an EQE<inf>max</inf> of 14.8% and CIE coordinates of (0.150, 0.044), which are very close to the BT.2020 requirement for blue pixels.

DOI： 10.1039/d2cc03347j

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PubMed

Language：English   Publisher：Chemical Science  

This work reports a new acceptor for constructing donor-acceptor type (D-A type) blue thermally activated delayed fluorescence (TADF) emitters with narrowed charge-transfer (CT) emissions. A new acceptor core, carbazole-2-carbonitrile (CCN), is formed by the fusion of carbazole and benzonitrile. Three D-A type TADF emitters based on the CCN acceptor, namely 3CzCCN, 3MeCzCCN, and 3PhCzCCN, have been successfully synthesized and characterized. These emitters show deep-blue emissions from 439 to 457 nm with high photoluminescence quantum yields of up to 85% in degassed toluene solutions. Interestingly, all CCN-based deep-blue TADF emitters result in narrow CT emissions with full-width at half-maximums (FWHMs) of less than 50 nm in toluene solutions, which are pretty narrower compared with those of typical D-A type TADF emitters. Devices based on these emitters show high maximum external quantum efficiencies of up to 17.5%.

DOI： 10.1039/d2sc02478k

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PubMed

Publisher：Advanced Optical Materials  

Thermally activated delayed fluorescence (TADF) emitters induced by the multiple resonance (MR) effect have garnered considerable attention. However, it is difficult to develop MR-TADF emitters that maintain high color purities in the red region. In this work, the importance of excited state alignments of MR-based donor-acceptor (D-A) molecules in determining their preferring characteristics is clarified. By using the newly designed molecule mBDPA-TOAT whose apparent excited states show hybridization of MR and intersegmental charge-transfer features as an emitter in an organic light-emitting diode (OLED), a high external quantum efficiency of 17.3% is achieved with a full width at half-maximum of 45 nm (154 meV) and Commission Internationale de L'Éclairage coordinate of (0.61, 0.39). This work demonstrates when introducing D-A typed structures, features, and alignments of molecular excited states determine ultimate material properties. This could help to develop high efficiency and high color purity TADF emitters toward long wavelength range.

DOI： 10.1002/adom.202101789

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Scopus

Publisher：Proceedings of SPIE the International Society for Optical Engineering  

Organic light-emitting diodes (OLEDs) are a promising light-emitting technology useful for various display applications1,2. Despite great progress in this field3-12, there is an ongoing challenge to realize high performance blue OLEDs with efficiency, good color purity, and device lifetime. Here, we report pure-blue (CIEx,y color coordinates of [0.13, 0.16]) OLEDs with high-efficiency (external quantum efficiency of 32 % at 1000 cd m-2), narrow-emission (full width half maximum of 19 nm), and good stability (LT95 of 18 hours at an initial luminance of 1000 cd m-2). The design is based on a two-unit stacked tandem hyperfluorescence (HF)-OLED with an improved singlet-excited energy transfer process from a sky-blue TADF assistant dopant (AD) (HDT-1) to a pure-blue terminal emitter (TE) (v-DABNA). Furthermore, the effect of dopant concentration of terminal emitter on the device performance of hyperfluorescence OLEDs is studied. Device shows a better color purity when dopant concentration is increased. On the other hand, new hyperfluorescence OLEDs have been fabricated, in which device stability has been extended with a new molecular design of TE.

DOI： 10.1117/12.2632333

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