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Organic scintillators have recently gained considerable attentions in X‐ray detection for their potential applications in biomedical radiograph and security inspection. However, the weak X‐ray absorption and/or inefficient exciton utilization have limited the development and commercialization of organic scintillators. Currently, high‐performance X‐ray organic scintillators are scarce and organic scintillators with dual triplet‐harvesting channels have not been explored before. Here, we develop several proof‐of‐concept sulfone‐based organic molecules, C1–C7, using different alkoxy chains to manipulate molecular packing mode. These materials exhibit dual triplet‐harvesting channels of thermally activated delayed fluorescence (TADF) and room‐temperature phosphorescence (RTP) in aggregated state. Inspiringly, these molecules display distinct radioluminescence under the X‐ray stimulation. Among them, C6 behaves the highest light yield of 16,558 photons MeV−1. Moreover, clear X‐ray images are demonstrated in both aggregated state and single‐molecule level. High spatial resolutions of 15.0 and 10.6 line pairs per millimeter (lp mm−1) are achieved for rigid and flexible scintillator screens, exceeding most reported organic and conventional inorganic scintillators. These results highlight the great potential of organic molecules with TADF and RTP nature for efficient X‐ray scintillation and imaging. [ABSTRACT FROM AUTHOR]

B/N‐based multi‐resonance thermally activated delayed fluorescence (MR‐TADF) emitters and the corresponding narrow band emissive organic light‐emitting diodes (OLEDs) exhibit great potential for next‐generation high‐resolution displays. Nonetheless, designing MR‐TADF emitters with emission wavelength over 550 nm remains challenging. Herein, an effective approach toward yellow‐to‐orange MR‐TADF emitters by integrating a strong electron‐donating indolophenazine building block into the B/N‐doped polycyclic aromatic hydrocarbons is proposed. The investigation of photophysical properties reveals that the electron‐donating difference between the donor segments of MR framework has a dramatic influence on the luminescent features, including the emission wavelength and full‐width at half‐maximum (FWHM). These TADF emitters display excellent photophysical characteristics such as near‐unity photoluminescence quantum yields and almost 100% horizontal dipole ratio. As a result, yellow and orange OLEDs employing these emitters achieve state‐of‐the‐art device performances with an ultrahigh external quantum efficiency of up to nearly 40%, power efficiency of 163 lm W−1, and luminance close to 120 000 cd m−2, which set a record among MR‐TADF based OLEDs with emission peaks over 550 nm. More impressively, the fabricated device presents outstanding operational stability of LT99 over 110 h at the initial brightness of 3000 cd m−2. [ABSTRACT FROM AUTHOR]

Multi‐resonance TADF (MR‐TADF) emitters are promising for high‐resolution OLEDs, but the concurrent optimization of excited‐state dynamics and color purity remains a tough challenge. Herein, three deep‐blue MR‐TADF compounds (BN1–BN3) featuring gradually enlarged ring‐fused structures and increased rigidity are accessed by lithium‐free borylation in high yields from the same precursor, with all the emitters possessing CIEy coordinates below 0.08. Structure–property investigations demonstrate a strategic improvement of the oscillator strength (fosc) and acceleration of the reverse intersystem crossing (RISC) process by extending the π‐skeleton, where BN3 realizes a maximum external quantum efficiency (EQE) of 37.6 % and reduced roll‐off, thus showing the best efficiency reported for deep‐blue TADF OLEDs. The internal regulation of the efficiency and color purity of these compounds validate the general effectiveness to achieve advanced deep‐blue narrowband emitters with higher‐order boron/nitrogen‐based MR motifs. [ABSTRACT FROM AUTHOR]

Multi‐layer π‐stacked emitters based on spatially confined donor/acceptor/donor (D/A/D) patterns have been developed to achieve high‐efficiency thermally activated delayed fluorescence (TADF). In this case, dual donor moieties and a single acceptor moiety are introduced to form two three‐dimensional (3D) emitters, DM‐BD1 and DM‐BD2, which rely on spatial charge transfer (CT). Owing to the enforced face‐to‐face D/A/D pattern, effective CT interactions are realized, which lead to high photoluminescence quantum yields (PLQYs) of 94.2 % and 92.8 % for the two molecules, respectively. The resulting emitters exhibit small singlet–triplet energy splitting (ΔEST) and fast reverse intersystem crossing (RISC) processes. Maximum external quantum efficiencies (EQEs) of 28.0 % and 26.6 % were realized for devices based on DM‐BD1 and DM‐BD2, respectively, which are higher than those of their D/A‐type analogues. [ABSTRACT FROM AUTHOR]

The development of red thermally activated delayed fluorescence (TADF) emitters having excellent optoelectronic properties and satisfactory electroluminescence efficiency is full of challenges due to strict molecular design principles. Two red TADF molecules, 3‐(9,9‐dimethylacridin‐10(9H)‐yl)acenaphtho[1,2‐b]quinoxaline‐9,10‐dicarbonitrile and 3‐(2,7‐dimethyl‐10H‐spiro[acridine‐9,9′‐fluoren]‐10‐yl)acenaphtho[1,2‐b]quinoxaline‐9,10‐dicarbonitrile, are developed by adopting a donor–acceptor molecular architecture bearing an electron‐accepting acenaphtho[1,2‐b]quinoxaline‐9,10‐dicarbonitrile (ANQDC) moiety and a 9,9‐dimethyl‐9,10‐dihydroacridine or 2,7‐dimethyl‐10H‐spiro[acridine‐9,9′‐fluorene] electron donor. The combined effects of rigid and planar D/A moieties and highly steric hindrance between D and A groups endow both molecules with high rigidity to suppress nonradiative decay processes, resulting in high photoluminescence quantum efficiencies (ΦPLs) of up to 95%. Attributed to the linear and planar acceptor motif and rod‐like molecular configuration, both emitters achieve high horizontal ratios of emitting dipole orientation of ≈80%. The organic light‐emitting diodes (OLEDs) based on both emitters exhibit red emissions peaking at ≈615 nm and successfully afford ultrahigh electroluminescence performance with an external quantum efficiency of nearly 28% and a power efficiency of above 50 lm W−1, on par with the state‐of‐the‐art device efficiency for red TADF OLEDs. This presents a feasible design strategy for excellent TADF emitters simultaneously possessing high ΦPLs and horizontally aligned emitting dipoles. [ABSTRACT FROM AUTHOR]

Although numerous thermally activated delayed fluorescence (TADF) organic light‐emitting diodes (OLEDs) have been demonstrated, efficient blue or even sky‐blue TADF‐based nondoped solution‐processed devices are still very rare. Herein, through‐space charge transfer (TSCT) and through‐bond charge transfer (TBCT) effects are skillfully incorporated, as well as the multi‐(donor/acceptor) characteristic, into one molecule. The former allows this material to show small singlet–triplet energy splitting (ΔEST) and a high transition dipole moment. The latter, on the one hand, further lights up multichannel reverse intersystem crossing (RISC) to increase triplet exciton utilization via degenerating molecular orbitals. On the other hand, the nature of the molecular twisted structure effectively suppresses intermolecular packing to obtain high photoluminescence quantum yield (PLQY) in neat flims. Consequently, using this design strategy, T‐CNDF‐T‐tCz containing three donor and three acceptor units, successfully realizes a small ΔEST (≈0.03 eV) and a high PLQY (≈0.76) at the same time; hence the nondoped solution‐processed sky‐blue TADF‐OLED displays record‐breaking efficiency among the solution process‐based nondoped sky‐blue OLEDs, with high brightness over 5200 cd m−2 and external quantum efficiency up to 21.0%. [ABSTRACT FROM AUTHOR]

Abstract: A new route to utilize the triplet excitons by simultaneous thermally activated delayed fluorescence (TADF) and phosphorescence is demonstrated for a new quinoxaline/phenoxazine hybrid emitter. Moreover, the two triplet recycling channels are thermally controlled, and a clear threshold temperature of 170 K is observed. Below the threshold temperature, direct triplet radiation (phosphorescence) is the dominant process. In contrast, the channel of upconversion through intersystem crossing is activated above the threshold and the resulting TADF gradually becomes the predominant process. By using the new compound as emitter in organic light‐emitting diodes, a high external quantum efficiency of 16.8% is far beyond the theoretical limit of the traditional fluorescent emitters. [ABSTRACT FROM AUTHOR]

A series of green butterfly-shaped thermally activated delayed fluorescence (TADF) emitters, namely PXZPM, PXZMePM, and PXZPhPM, are developed by integrating an electron-donor (D) phenoxazine unit and electron-acceptor (A) 2-substituted pyrimidine moiety into one molecule via a phenyl-bridge π linkage to form a D-π-A-π-D configuration. Changing the substituent at pyrimidine unit in these emitters can finely tune their emissive characteristics, thermal properties, and energy gaps between the singlet and triplet states while maintaining frontier molecular orbital levels, and thereby optimizing their optoelectronic properties. Employing these TADF emitters results in a green fluorescent organic light-emitting diode (OLED) that exhibits a peak forward-viewing external quantum efficiency (EQE) close to 25 % and a slow efficiency roll-off characteristic at high luminance. [ABSTRACT FROM AUTHOR]

Through‐space charge transfer, which exists in nonconjugation linker based thermally activated delayed fluorescence (TADF) materials, excites chemists to explore more possibilities in organic light‐emitting diodes (OLEDs). Herein, an sp3‐hybrid carbon‐centered donor–σ–acceptor type chromophore, QAFCN, is tentatively developed by exploring bi‐acridine based electron‐donor, i.e., 5,5‐dimethyl‐5,9‐dihydroquinolino[3,2,1‐de]acridine (QA). It is interesting to find that the QA moiety shows downshift in highest occupied molecular orbital because of its deformed geometry, which makes it qualified for sky‐blue electroluminescence emission. Together with the blue‐shift, enhanced photoluminescence quantum yield and faster reverse intersystem crossing rate are also observed in QAFCN, which can be attributed to the close through‐space distance between donor/acceptor. As compared to the ACRFLCN without these special features, QAFCN has obvious TADF property and achieves efficient OLEDs of ≈18% external quantum efficiency. [ABSTRACT FROM AUTHOR]

Butterfly ‐ shaped green ‐ emissive fluorescence emitters on the basis of pyrimidine/phenoxazine hybrids have been developed and utilized as dopants in high ‐ efficiency organic light ‐ emitting diodes. The thermally activated delayed fluorescence (TADF) feature of these emitters makes the recruitment of transition ‐ forbidden triplet excitons feasible through the reverse intersystem ‐ crossing process of T1→S1. More information can be found in the Full Paper by S. Gong, J. Jiang, C. Yang et al. on page 10860. [ABSTRACT FROM AUTHOR]

We designed and synthesized a series of new butterfly-shaped D-A-D type compounds with quinoxaline as an electron acceptor. Their photoluminescence (PL) spectra are successfully tuned from green to orange based on the intramolecular charge transfer effect. Moreover, through theoretical and experimental approaches, we have verified the dihedral angles between the donor and acceptor, the value of ΔE ST and the nature of T 1 play crucial roles in shaping the emissive properties, and we have also successfully tuned the emission type from local excited-state (LE) to charge-transfer state (CT) transition to acquire a TADF molecule. A high rate constant for reverse intersystem crossing (RISC) is up to 1.5 × 10 6 s −1 . The BDQDMAC-based orange TADF OLEDs exhibit a maximum external quantum efficiency of 7.4%, corresponding to a prominent contribution of 97% from the delayed fluorescence to the overall external quantum efficiency. [ABSTRACT FROM AUTHOR]

Two fluorescent emitters, 3DMACIPN and 4DMACIPN, bearing an isophthalonitrile unit as an acceptor core and multiple 9,9-dimethyl-9,10-dihydroacridine donor moieties were designed and synthesized. These emitters feature high thermal stability and thermally activated delayed fluorescence characteristics with relatively short delayed lifetimes (0.99 and 1.69 μs for 3DMACIPN and 4DMACIPN, respectively). By employing these TADF emitters doped into 4,4′-Bis( N -carbazolyl)-1,1′-biphenyl host as emissive layers, a green OLED achieved a maximum EQE of 10.0% and slow efficiency roll-off at a high luminance. [ABSTRACT FROM AUTHOR]

[Display omitted] • A typical TADF emitter was served as the humidity-responsive sensor for the first time. • Applications in erasable paper and fingerprint identification were demonstrated in a visible way. • Hydrogen bond was proved to play a crucial role in the humidity-response property. Humidity monitoring is of great importance in our daily life and industrial process. However, humidity sensors based on fluorescent materials are usually hybrid system, which inevitably causes poor stability and bad repeatability. Herein, a conceptually new class of humidity-responsive thermally activated delayed fluorescent (TADF) material, AcHPM, is presented. AcHPM displays significant emission color changes from deep blue (446 nm) to green (510 nm) under different relative humidity (RH) from 1 % to 95 %. In addition to the high contrast of fluorescent emission (>60 nm), the AcHPM-sensor also shows ultrafast response time (about 20 ms) and good reversibility (>10 cycles). In view of the excellent humidity-responsive performance of AcHPM, the potential application of real-time RH monitoring, anti-counterfeiting, and fingerprint identification were presented by using an AcHPM-equipped test paper. To disclose the mechanism behind the humidity-dependent fluorescence, we further carry out the Fourier transform infrared spectroscopy, powder X-ray diffraction, and theoretical simulation, which jointly verify the critical role of hydrogen bond between water and AcHPM molecule. This work not only extends an avenue to develop humidity sensor with single component for various applications in our daily life, but also provides a new sight to explore the mechanism for the fluorescent-responsive processes. [ABSTRACT FROM AUTHOR]

[Display omitted] • Narrowband green emitters are successfully achieved by multi-resonance boron-nitrogen framework. • Heavy-atom effect of sulfur was beneficial to accelerate the reverse intersystem crossing. • Green organic light-emitting diodes with high external quantum efficiency up to 25.5% are achieved. As one type of latest emitters with simultaneous high efficiency and color-purity, the development of multi-resonance thermally activated delayed fluorescence (MR-TADF) materials represents an important advancement for organic light-emitting diodes (OLEDs). We herein present a new strategy to improve the performance of MR-TADF emitters by fusing sulfur element into the B-N based framework, aiming to utilize the non-metal heavy-atom effect in accelerating the reverse intersystem crossing (RISC) process of the emitter. Two compounds, namely 2PTZBN and 2PXZBN, were developed in this work through rigidifying the DABNA-1 skeleton by sulfur or oxygen atoms. The theoretical calculations and photoluminescence studies reveal that the sulfur-incorporated 2PTZBN enable considerable rate constant of RISC (k RISC) up to 2.8 × 105 s−1 in toluene due to larger spin-orbital coupling (SOC) values and smaller singlet–triplet energy splitting (Δ E ST) compared with 2PXZBN. Consequently, organic light-emitting diodes based on 2PTZBN exhibited highly efficient green emission with maximum external quantum efficiency (EQE) of 25.5%. [ABSTRACT FROM AUTHOR]