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Embedding donor–acceptor type thermally activated delayed fluorescence (TADF) molecules in a rigid surrounding lead to structural inhomogeneity, and deteriorating emission decay rates. Designing TADF structures with hampered rotational flexibility between donor and acceptor structural units is shown to lower the conformational disorder. However, in this work, it is shown that it is not always enough. In fact, the negative impact of conformational inhomogeneity may be reduced by lowering the singlet‐triplet energy gap (ΔEST) and boosting the reverse intersystem crossing (rISC) rate while preserving the same donor‐acceptor orientation. In such cases the lower ΔEST enables the early triplet upconversion even from the conformers with unfavorably low D‐A twist angles, which is not observed in compounds with larger ΔEST. In this way, the temporal shifts of prompt and delayed fluorescence are evidently reduced. When the reverse intersystem crossing is inactive at low temperatures, nearly the same fluorescence peak shifts are observed, as expected for compounds with similar molecular geometry. In this way, low ΔEST and rapid rISC are shown to be of fundamental importance not only for TADF efficiency but also for the temporal dynamics in the solid‐state. [ABSTRACT FROM AUTHOR]

Although two‐coordinate Cu(I) complexes are highly promising low‐cost emitters for organic light‐emitting diodes (OLEDs), the exposed metal center in the linear coordination geometry makes them suffer from poor stability. Herein, we describe a strategy to develop stable carbene‐Cu‐amide complexes through installing intramolecular noncovalent Cu⋅⋅⋅H interactions. The employment of 13H‐dibenzo[a,i]carbazole (DBC) as the amide ligand leads to short Cu⋅⋅⋅H distances in addition to the Cu−N coordination bond. The resultant Cu(I) complexes exhibit yellow thermally activated delayed fluorescence with photoluminescence quantum yields of up to 86 % and radiative decay rate constants on the order of 106 s−1. Comparing with the analogues without Cu⋅⋅⋅H interactions, the pincer complexes have significantly improved stability. The vacuum‐deposited OLEDs show high‐performance electroluminescence with maximum external quantum efficiencies of up to 29.5 % and extremely small roll‐offs of only 3.5 % at 10,000 cd m−2. Remarkably, the operational lifetimes (LT90) are up to 68 h with an initial luminance of 3000 cd m−2. This work proves a feasible design of robust low‐coordinate metal complexes by leveraging secondary coordination interactions, which helps to overcome the long‐standing stability problem. [ABSTRACT FROM AUTHOR]

Thermally activated delayed fluorescence (TADF) materials are expected to address triplet‐related losses in electrically driven organic lasers, as the electrically generated triplets in the materials can be converted to radiative singlets through reverse intersystem crossing (RISC). This offers a way to bypass triplet absorption and annihilation in organic semiconductor lasers (OSLs). In this work, two versatile TADF emitters 4tCzPz and 4αCbPz for application in organic light‐emitting diodes (OLEDs) and OSLs are presented. Both emitters possess moderately high singlet‐triplet energy gap, ΔEST (≈0.30 eV) and show high photoluminescence quantum yields, ΦPL, in solution and solid‐state and prominent stimulated emission features in solution. Films of 4tCzPz and 4αCbPz doped in mCBP show an amplified spontaneous emission (ASE) threshold of 41.0 and 44.9 µJ/cm2, respectively. The OLEDs with 4tCzPz and 4αCbPz emit with peak wavelengths of 492 and 475 nm, respectively, and show corresponding maximum external quantum efficiencies, EQEmax, of 24.6 and 21.3%. The research shows that D‐A TADF materials hold significant potential not only as emitters for OLEDs but also in OSLs. [ABSTRACT FROM AUTHOR]

Achieving a wide‐range color‐tunable and dynamically long‐afterglow emission in a single‐doped system remains a challenge. In this study, a unique host‐guest doped material, TPA‐PTPQ/TPA, exhibits dual‐delay emission at 516 and 605 nm, both with long lifetimes of up to 108 and 145 ms, which derives from thermally activated delayed fluorescence (TADF) and room temperature phosphorescence (RTP) mechanisms, respectively. Notably, this host‐guest material demonstrates a temperature‐dependent dynamically reversible afterglow characteristic, transitioning green, orange, and red with a substantial spectra shift of ≈90 nm under different temperature conditions. This phenomenon is due to the diverse temperature effect on TADF and RTP emissions. These remarkable luminescence properties are successfully applied in security checks and anti‐counterfeiting encryption. This study provides valuable insights into the design of dynamically reversible dual‐delay‐emissive long‐afterglow luminescent materials based on a host‐guest doping system. [ABSTRACT FROM AUTHOR]

Photodynamic therapy (PDT) represents a novel, dual‐stage cancer treatment approach that combines light energy and photosensitizers to destroy cancerous and precancerous cells through the generation of radicals (Type I) or singlet oxygen (Type II). Since the early 2010s, PDT has advanced significantly, with the focus shifting toward the exploration of molecules capable of thermally activated delayed fluorescence (TADF) as viable alternatives to traditional metallic complexes and organometallic compounds for producing the necessary active species. TADF molecules exhibit higher energy conversion efficiency, long‐lived triplet excitons, tunable photophysical properties, and a small singlet‐triplet energy gap, facilitating efficient intersystem crossing and enhanced singlet oxygen generation. As metal‐free luminophores, they offer benefits such as reduced health risks, high structural flexibility, and biocompatibility, which can significantly enhance PDT treatment efficacy. Notably, in 2019, a pivotal shift occurred, with researchers concentrating their efforts on identifying and investing in potential molecules specifically for Type II PDT applications. This review presents the innovative use of materials characterized by closely spaced S1 and T1 orbitals, crucial for the efficient generation of singlet oxygen in PDT. Exploring these materials opens new avenues for enhancing the efficacy and specificity of PDT, offering promising for future cancer treatments. [ABSTRACT FROM AUTHOR]

Thermally activated delayed fluorescence (TADF) materials have attracted considerable interest due to their ability to enhance electrochemiluminescence (ECL). This is achieved through the efficient upconversion of triplet excitons and the subsequent radiative transitions. However, despite the potential of TADF materials, there have been few studies exploring their application in ECL field. Accordingly, in this concept, a number of TADF materials, which can be categorized into two principal groups based on intramolecular bond charge transfer and intermolecular space charge transfer, are introduced in order to explore the potential for their application in ECL. A brief review of their properties not only helps to deepen the understanding of the nature of TADF materials, but also provides basic guidance and support for the introduction of the TADF mechanism into ECL systems, with the aim of enhancing the luminescence efficiency of ECL. [ABSTRACT FROM AUTHOR]

Organic scintillators are praised for their abundant element reserves, facile preparation procedures, and rich structures. However, the weak X‐ray attenuation ability and low exciton utilization efficiency result in unsatisfactory scintillation performance. Herein, a new family of highly efficient organic phosphonium halide salts with thermally activated delayed fluorescence (TADF) are designed by innovatively adopting quaternary phosphonium as the electron acceptor, while dimethylamine group and halide anions (I−) serve as the electron donor. The prepared butyl(2‐[2‐(dimethylamino)phenyl]phenyl)diphenylphosphonium iodide (C4‐I) exhibits bright blue emission and an ultra‐high photoluminescence quantum yield (PLQY) of 100 %. Efficient charge transfer is realized through the unique n‐π and anion‐π stacking in solid‐state C4‐I. Photophysical studies of C4‐I suggest that the incorporation of I accounts for high intersystem crossing rate (kISC) and reverse intersystem crossing rate (kRISC), suppressing the intrinsic prompt fluorescence and enabling near‐pure TADF emission at room temperature. Benefitting from the large Stokes shift, high PLQY, efficient exciton utilization, and remarkable X‐ray attenuation ability endowed by I, C4‐I delivers an outstanding light yield of 80721 photons/MeV and a low limit of detection (LoD) of 22.79 nGy ⋅ s−1. This work would provide a rational design concept and open up an appealing road for developing efficient organic scintillators with tunable emission, strong X‐ray attenuation ability, and excellent scintillator performance. [ABSTRACT FROM AUTHOR]

Organic light-emitting diodes are constantly developed technologically. An advantageous strategy for efficient work of the devices is the design of emitters exhibiting thermally activated delayed fluorescence (TADF). Efforts are invested, especially towards blue TADF fluorophores. The complex nature of the involved photophysical processes prohibits straightforward prediction of dyes with enhanced TADF potential. Design rules are knowledge-based or derived for specific cases. In the present work, we attempt to establish quantitative structure–property relationships (QSPR) between a key optical property of potential TADF emitters and a set of molecular descriptors. The goal is a statistical model providing better understanding of the molecular factors governing the excited states singlet–triplet energy splitting. We utilise multiple linear regression and principal component analysis to correlate the values of the excited singlet–triplet energy gap to various molecular characteristics. The validated models demonstrate the complexity and collective nature of TADF events and highlight the essential role of the electron-donor fragment. [ABSTRACT FROM AUTHOR]

Hot exciton emitters based on 9,10‐substituted anthracenes are a well‐investigated class of molecules featuring thermally activated delayed fluorescence (TADF). TADF converts triplet excitons into singlet excitons and improves the internal quantum efficiency of electroluminescent devices to performance beyond the limit of spin‐statistics of conventional emitters. In this paper, we compare different 1,8‐functionalized donor/acceptor‐substituted anthracenes and compare these to established 9,10‐functionalized hot exciton emitters. Interestingly, our new 1,8‐substituted anthracenes make use of a beneficial hot exciplex pathway, resulting in improved emission characteristics and higher photoluminescence quantum yield. [ABSTRACT FROM AUTHOR]

Spiro structures, possessing unique π‐electron systems, large steric hindrance, high glass transition temperature, and chemical stability, serve as critical structural building blocks in constructing thermally activated delayed fluorescence (TADF) emitters. The incorporation of various heteroatoms such as oxygen, sulfur, and nitrogen in 9,9′‐spirobifluorene generates diverse spiro structures like spiro[fluorene‐9,9′‐xanthene], spiro[fluorene‐9,9′‐thioxanthene], and spiro[acridine‐9,9′‐fluorene]. Based on the charge transfer characteristics, TADF emitters built upon spiro structures can be classified into various types, including twisted intramolecular charge transfer, through‐space charge transfer, multiresonance, and exciplex‐type TADF emitters. This review systematically highlights the recent progress in the research on TADF emitters comprised of spiro‐structured aromatics. It intricately explores the molecular design strategies, material synthesis methods, understanding of photophysical attributes, and analysis of organic light‐emitting diode performance. Concurrently, it sketches out the challenges faced in the commercial application stage while providing an outlook for potential research trajectories. [ABSTRACT FROM AUTHOR]

Thermally activated delayed fluorescence (TADF) materials have garnered significant attention in developing high-efficiency organic light-emitting diodes (OLEDs) for next-generation displays. Despite the progress in TADF research, the increasing complexity of molecular structures poses challenges in material design and synthesis. This study explores the potential of quantitative structure–activity relationship (QSAR) calculations, particularly AutoQSAR, to streamline TADF OLED material selection and design. By leveraging the predictive capabilities of QSAR, we aimed to enhance the accuracy and efficiency of material development. We employed computational modeling, synthesis, and device fabrication to evaluate the performance of a newly developed green TADF dopant material. Our findings indicate that QSAR-guided design predicts material properties effectively and optimizes OLED performance. The synthesized TADF material demonstrated promising efficiency, highlighting the advantages of integrating QSAR calculations into the material discovery process. This study underscores the feasibility of QSAR methodologies in the context of OLED materials, suggesting a pathway for faster and more accurate development. Future improvements in QSAR techniques and collaborative efforts between computational and experimental research will be essential in driving further advancements in OLED technology.

Thermally activated delayed fluorescence (TADF)‐based materials are attracting widespread attention for different applications owing to their ability of harvesting both singlet and triplet excitons without noble metals in their structures. As compared to the conventional fluorescence and room‐temperature phosphorescence pathways, TADF originates from the reverse intersystem crossing process from the excited triplet state (T1) to the singlet state (S1). Therefore, TADF emitters enabling activated and long lifetime T1 excitons are potential candidates for generating long‐lived afterglow emission, an effect that can still be observed for a while by the naked eye after the removal of the excitation light source. Recently, TADF‐based organic afterglow materials featuring high photoluminescence quantum yields and long lifetimes above 100 ms under ambient conditions, have emerged for advanced information security, high‐contrast biological imaging, optoelectronic devices, and intelligent sensors, whereas the related systematic review is still lacking. Herein, the recent progress in TADF‐based organic afterglow materials is summarized and an overview of the photophysical mechanism, design strategies, and the performances for relevant applications is given. In addition, the challenge and perspective of this area are given at the end of the review. [ABSTRACT FROM AUTHOR]

Tetrahydro-4H-thiopyran-4-one 1-oxide 1 and sulfinyl-di-tert-butylpropionate 2 were reported as sources of bis-sulfenate anion and applied in a double pallado-catalyzed cross-coupling reaction for the synthesis of symmetrical biarylsulfoxides, tolerating a large array of electronic properties and bulkiness. The photophysical properties of a biarylsulfoxide have been explored, demonstrating an unreported TADF phenomenon on sulfoxide-containing scaffolds. [ABSTRACT FROM AUTHOR]

To enhance organic light emitting diode (OLED) performance, host materials with high triplet energies are crucial for confining excitons, despite increasing driving voltages due to the singlet‐triplet energy gap. We synthesized sulfonylbis(4,1‐phenylene)bis(3,6‐disubstituted‐9H‐carbazole) derivatives as donor‐acceptor‐donor host materials, namely compounds 3, 5 and 7, with varying fluorination levels. These compounds show moderate singlet‐triplet energy splitting and molecular dipole moments, allowing for fine‐tuning of hole‐transport mobilities, deeper frontier orbital energies, and a red shift in singlet emission while maintaining high triplet energy levels. These adjustments impact a range of physical, electronic and optical properties. The materials exhibit exceptional thermal stability, with decomposition starting above 400 °C and glass transition temperatures over 130 °C. Used with the green TADF emitter DACT‐II, these hosts enable reverse intersystem crossing rates between 7.43×104 s−1 and 1.77×105 s−1. While OLEDs using mCP as a reference host achieve a maximum quantum efficiency of 18.5 %, those with host 5 show lower efficiency roll‐off, leading to higher external quantum efficiency at brightness levels above 2000 cd/m2 without colour shift. The reduced roll‐off in devices with host 5 compared to mCP is attributed to effective Förster and Dexter energy transfers to DACT‐II at high currents, enhancing light emission pathways. [ABSTRACT FROM AUTHOR]

Multiresonant thermally activated delayed fluorescence (MR‐TADF) emitters have been the focus of extensive design efforts as they are recognized to show bright, narrowband emission, which makes them very appealing for display applications. However, the planar geometry and relatively large singlet–triplet energy gap lead to, respectively, severe aggregation‐caused quenching (ACQ) and slow reverse intersystem crossing (RISC). Here, a design strategy is proposed to address both issues. Two MR‐TADF emitters triphenylphosphine oxide (TPPO)‐tBu‐DiKTa and triphenylamine (TPA)‐tBu‐DiKTa have been synthesized. Twisted ortho‐substituted groups help increase the intermolecular distance and largely suppress the ACQ. In addition, the contributions from intermolecular charge transfer states in the case of TPA‐tBu‐DiKTa help to accelerate RISC. The organic light‐emitting diodes (OLEDs) with TPPO‐tBu‐DiKTa and TPA‐tBu‐DiKTa exhibit high maximum external quantum efficiencies (EQEmax) of 24.4% and 31.0%, respectively. Notably, the device with 25 wt% TPA‐tBu‐DiKTa showed both high EQEmax of 28.0% and reduced efficiency roll‐off (19.9% EQE at 1000 cd m−2) compared to the device with 5 wt% emitter (31.0% EQEmax and 11.0% EQE at 1000 cd m−2). The new emitters were also introduced into single‐layer light‐emitting electrochemical cells (LECs), equipped with air‐stable electrodes. The LEC containing TPA‐tBu‐DiKTa dispersed at 0.5 wt% in a matrix comprising a mobility‐balanced blend‐host and an ionic liquid electrolyte delivered blue luminance with an EQEmax of 2.6% at 425 cd m−2. The high efficiencies of the OLEDs and LECs with TPA‐tBu‐DiKTa illustrate the potential for improving device performance when the DiKTa core is decorated with twisted bulky donors. [ABSTRACT FROM AUTHOR]

Non‐conjugated luminescent polymers have received much attention due to their excellent flexibility, processability, and biocompatibility. However, the single emission color and low solid‐state luminescence efficiency restrict their further development. Herein, by introducing carboxyl‐terminated alkyl chains on the rigid and helical polymaleimide backbone, a series of non‐conjugated luminescent polymers are designed and synthesized. Due to the "spring lock" formed by the synergism of scalable helical main chains and flexible alkyl side chains, these polymers exhibit effective cluster luminescence with thermally activated delayed fluorescence (TADF) property, thereby significantly improving the solid‐state luminescence efficiency with the quantum yield up to 59.6%. The TADF emission wavelengths of the polymer powders can be tuned from 498 to 639 nm through changing reaction solvents, because the conformation of helical chains forming clusters is sensitive to solvent polarity. Interestingly, metal ions can induce the polymers to construct self‐repairing cluster luminescence gels, which show excellent potential applications in ammonia detection and information encryption. This work not only provides an effective design strategy for the colorful cluster luminescence with high‐efficiency TADF, but also further reveals the cluster luminescence mechanism and enlightens the promising applications of cluster luminescent gels. [ABSTRACT FROM AUTHOR]

Recent advances in organic light‐emitting diodes (OLEDs) based on thermally activated delayed fluorescence (TADF)‐assisted fluorescence (TAF) attest to the great promise of this technology in practical use. However, the simultaneous realization of high efficiency and device durability in blue OLEDs remains a significant challenge. Clarification of the degradation mechanisms correlated to molecular structure and device configuration is the key to extending the device lifetime. In this study, electron transport materials incorporating two triazine units in close proximity are adopted to use in hole‐blocking and electron‐transporting layers, resulting in superior device performances. In addition, a modified photodegradation experiment reveals that the degradation origins closely relate to charge carriers. The optimization of the device according to the obtained findings leads to 4.5 times extension in the lifetime of the TAF‐OLED using a multiple resonance emitter. These results also provide guidelines for designing robust electron transport materials for blue OLEDs. [ABSTRACT FROM AUTHOR]

Materials exhibiting thermally activated delayed fluorescence (TADF) based on transition metal complexes are currently gathering significant attention due to their technological potential. Their application extends beyond optoelectronics, in particular organic light‐emitting diodes (OLEDs) and light‐emitting electrochemical cells (LECs), and include also photocatalysis, sensing, and X‐ray scintillators. From the perspective of sustainability, earth‐abundant metal centers are preferred to rarer second‐ and third‐transition series elements, thus determining a reduction in costs and toxicity but without compromising the overall performances. This review offers an overview of earth‐abundant transition metal complexes exhibiting TADF and their application as photoconversion materials. Particular attention is devoted to the types of ligands employed, helping in the design of novel systems with enhanced TADF properties. [ABSTRACT FROM AUTHOR]

[Display omitted] Copolyfluorenes have drawn considerable attention owing to their remarkable optoelectronic characteristics, chemical and thermal stability, good film-forming properties, and thus present an active subject of cutting-edge research in the organic electroluminescence. This current systematic review examines and summarizes the latest research on copolyfluorene-based materials for light emitting layers of OLEDs over the past decades. [ABSTRACT FROM AUTHOR]

Understanding thermally activated delayed fluorescence (TADF) in solid‐state environments is crucial for practical applications. However, limited research focuses on how the medium affects TADF properties of hot‐exciton‐based emitters. In our study, we calculated and compared reverse intersystem crossing, radiative, and non‐radiative decay rates of TADF emitters in gas, solvent, and solid phases. The designed emitters have a donor‐acceptor‐donor (D‐A‐D) structure, with donors such as triphenylamine (TPA) and diphenylamine thiophene (ThPA), combined with acceptors such as benzothiadiazole (BT), pyridine thiadiazole (PT) and thiadiazolobenzopyridine (NPT). We model the solvent and solid phases with the polarizable continuum model (PCM) and quantum mechanical/molecular mechanics (QM/MM) methods, respectively. Using density functional theory (DFT) and time‐dependent DFT, we analyze how TADF emitters′ geometrical, electronic, and excited‐state properties vary in these phases. Our results show that the solid‐state environment significantly influences the geometry and TADF properties of emitters. In the presence of solid medium, our study indicates that non‐radiative decay rates tend to be slower. On the other hand, radiative emission rates were found to be less influenced by the properties of the surrounding medium. Overall, our study connects emitter chemical structure and the surrounding environment's impact on excited‐state characteristics and photochemical properties. [ABSTRACT FROM AUTHOR]

Multi‐resonant thermally activated delayed fluorescent (MR‐TADF) materials, which combine large oscillator strengths, small singlet‐triplet energy gaps, high photoluminescence quantum yields, and color purity, have attracted great interest in both experimental and theoretical research in recent years. However, the differences between two classes of MR‐TADF, utilizing carbonyl groups and boron atoms as acceptors respectively, have not been clearly delineated, and the implementation of strategies combining both is extremely limited. This limitation hampers the diversity in composition and structure of MR‐TADF. In this study, we employed boron as the central acceptor and carbonyl groups as peripheral acceptors, designing and investigating 7 merged systems of MR‐TADF molecules. Calculations revealed that, in contrast to the strong acceptor characteristics of boron atoms, carbonyl groups do not exhibit absolute acceptor features, and their resonance effects depend on the surrounding environment. This unique resonance effect induces LRCT features to varying degrees, enabling the emission coverage of these molecules across almost the entire visible spectrum (theoretical emission wavelengths covering 452–751 nm). We gained an understanding of the differences between boron acceptors and carbonyl groups, achieving full‐color emission by adjusting only the MR cores. This provides insights into the rational design of complex‐component full‐color MR‐TADF emitters. [ABSTRACT FROM AUTHOR]

Considering that regulation of thermally activated delayed fluorescence (TADF) and room temperature phosphorescence (RTP) is necessary for a fluorophore to survive and properly show its characteristic features, it is successfully shown herein that a carefully designed novel pyrene derivative can exhibit remarkable aggregation‐induced emission (AIE) overcoming the characteristic fast excitonic decay of pyrene compounds. Moreover, it is established that J‐aggregation in the red‐emitting molecular crystals of the compound reduces the singlet‐triplet energy gap (∆EST), allowing TADF with a very high photoluminescence quantum yield (PLQY) of 72%. Whereas, anisotropic grinding of the same crystals generates well‐defined microcrystals that show RTP as the nature of aggregation changes. Impressively, under isotropic hydrostatic pressure, the crystals show near‐infra‐red (NIR) emission with a very high piezochromic luminescence sensitivity of 46.2 nm GPa−1. The results have established that formation of stable H‐aggregates in the microcrystals is responsible for the ultra‐long RTP. A highly sophisticated full‐spectrum Mueller‐matrix analysis is used for the first time in such systems to demonstrate the details of the effect of perturbation (pressure) on molecular conformation. [ABSTRACT FROM AUTHOR]

Mechanochromic luminescence materials have recently attracted increasing interest due to its promising applications, but the intensive inquiry of the mechanochromic luminescence mechanism is still insufficient. Herein, an in‐depth study of mechanochromic luminescent copper iodide complexes exhibiting ligand detachment and structural transformation is reported. The yellowish–green emissive CuI(dmpz) (dmpz = 2,6‐dimethylpyrazine) is ground into orange–red emissive CuI(dmpz)0.5 and the detailed structural transformation process is revealed by the thorough analysis of the crystalline structure before and after grinding. More importantly, new insight into the mechanochromic luminescence mechanism is proposed, that is, under the external force of grinding, the dmpz ligand detachment triggers the structural transformation from 1D chain to 2D network, which leads to the reduction of band gap energy and contraction of Cu─Cu bonds, together resulting in the red shift of luminescence ultimately. Moreover, the two complexes are also found to have thermochromic luminescence properties, attributing to their thermally activated delayed fluorescence process. The anti‐counterfeiting application of CuI(dmpz) is tentatively explored, demonstrating the favorable application prospect of CuI(dmpz). This study provides new insights involved in the mechanochromic luminescence mechanism of copper iodide complexes, and may provide a new understanding for rational molecular design and structural regulation of intelligent responsive luminescence. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

It is of great importance and worthy of efforts to give a clear structure–property relationship and microscopic mechanism of fluorescence emitters with high quantum yield. In this work, we perform a detailed computational investigation to give an explanation to the high efficiency of a fluorescence emitter XBTD‐NPh based TADF sensitized fluorescence (TSF) OLEDs, and construct a symmetry structure DSBNA‐BTD. Theoretical calculations show that XBTD‐NPh is a long‐time phosphorescent material at 77 K and TADF is attributed to the RISC of T1 to S1 state. For DSBNA‐BTD, excitons arrived at T1 state comes to a large rate of nonradiatively path to the ground state, meaning it is may not be an efficient TADF molecule. For both molecules, the fast IC between T2 and T1 state results in that the hot exciton channel T1‐Tn‐S1 makes no contribution to the TADF. [ABSTRACT FROM AUTHOR]

Thermally activated delayed fluorescence (TADF) is an emission mechanism whereby both singlet and triplet excitons can be harvested to produce light. Significant attention is devoted to developing TADF materials for organic light‐emitting diodes (OLEDs), while their use in other organic electronics applications such as sensors, has lagged. A family of TADF emitters, TPAPyAP, TPAPyBP, and TPAPyBPN containing a triphenylamine (TPA) donor and differing nitrogen‐containing heterocyclic pyrazine‐based acceptors is developed and systematically studied. Depending on the acceptor strength, these three compounds emit with photoluminescence maxima (λPL), of 516, 550, and 575 nm in toluene. Notably, all three compounds show a strong and selective spectral response to the presence of ZnCl2, making them the first optical TADF sensors for this analyte. It is demonstrated that these three emitters can be used in vacuum‐deposited OLEDs, which show moderate efficiencies. Of note, the device with TPAPyBPN in 2,8‐bis(diphenyl‐phoshporyl)‐dibenzo[b,d]thiophene (PPT) host emits at 657 nm and shows a maximum external quantum efficiency (EQEmax) of 12.5%. This electroluminescence is significantly red‐shifted yet shows comparable efficiency compared to a device fabricated in 4,4′‐bis(N‐carbazolyl)‐1,1′‐biphenyl (CBP) host (λEL = 596 nm, EQEmax = 13.6%). [ABSTRACT FROM AUTHOR]

Developing efficient long‐wavelength thermally activated delayed fluorescence (TADF) emitters is a challenging issue due to inherent limitations of the energy‐gap law. In this contribution, a new molecular design of cyanobenzene‐decorated quinoxaline acceptor, combining two or four cyanobenzene acceptors and a rigid carbazole donor, is successfully utilized to construct long‐wavelength TADF emitters (tCzQx2CN and tCzQx4CN). The two additional cyanobenzene units at the 5‐ and 8‐positions of the quinoxaline acceptor are presumed to interlock the molecular rotations and improve the acceptor strength. Compared with tCzQx2CN, tCzQx4CN exhibits orange‐red emission with a considerable bathochromic shift (>35 nm), as expected. Owing to its enhanced charge transfer and well‐separated highest‐occupied and lowest‐unoccupied molecular orbitals, tCzQx4CN exhibits reduced singlet‐triplet energy splitting and improves reverse intersystem crossing. An organic light–emitting diode (OLED) of tCzQx4CN manifestes bright orange‐red emission (λEL ≈581 nm), a superior external quantum efficiency (EQE) of ≈23.7% (compared with that of tCzQx2CN), and a satisfactory operational lifetime. Furthermore, a tCzQx4CN‐sensitized red‐hyperfluorescent OLED device exhibits excellent performance with an EQE of 16.0% and a CIE(x,y) of (0.62, 0.37). This design would potentially pave the way for constructing red/deep‐red TADF emitters by using a diverse combination of donor/acceptor units. [ABSTRACT FROM AUTHOR]

Förster resonance energy transfer (FRET) has been widely applied in fluorescence imaging, sensing and so on, while developing useful strategy of boosting FRET efficiency becomes a key issue that limits the application. Except optimizing spectral properties, promoting orientation factor (κ2) has been well discussed but rarely utilized for boosting FRET. Herein, we constructed binary nano‐assembling of two thermally activated delayed fluorescence (TADF) emitters (2CzPN and DMAC‐DPS) with J‐type aggregate of cyanine dye (C8S4) as doping films by taking advantage of their electrostatic interactions. Time‐resolved spectroscopic measurements indicated that 2CzPN/Cy‐J films exhibit an order of magnitude higher kFRET than DMAC‐DPS/Cy‐J films. Further quantitative analysing on kFRET and kDET indicated higher orientation factor (κ2) in 2CzPN/Cy‐J films play a key role for achieving fast kFRET, which was subsequently confirmed by anisotropic measurements. Corresponding DFT/TDDFT calculation revealed strong "two‐point" electrostatic anchoring in 2CzPN/Cy‐J films that is responsible for highly orientated transitions. We provide a new strategy for boosting FRET in nano‐assemblies, which might be inspired for designing FRET‐based devices of sensing, imaging and information encryption. [ABSTRACT FROM AUTHOR]

We introduce inverse design strategy utilizing machine learning (ML) models to discover efficient blue thermally activated delayed fluorescence (TADF) organic emitter materials. Here, we leverage graph neural network (GNN) to predict the characteristic intrinsic materials properties of TADF such as excited state energy levels and their transition properties. The GNN model is trained based on density‐functional theory (DFT) calculation results to meet the TADF properties. We discuss consistency between experimental observation and ML predictions, and examined conditions for improving the accuracy of DFT calculations and ML models on top of it. [ABSTRACT FROM AUTHOR]

In this article, we demonstrate that, by appropriately introducing inert substituents at the periphery of multi‐resonance fluorescent dye, charge trapping introduced by fluorescent dyes can be significantly inhibited in phosphor‐assisted fluorescence devices, and the energy transfer from assisted phosphor to fluorescent dyes can also be more efficient. [ABSTRACT FROM AUTHOR]

The development of OLED materials by molecular design is important for high performance organic light emitting diode because tailoring the molecular structures can dramatically tune the properties such as efficiency, color, stability of device. Near‐infrared organic light‐emitting diodes (NIR OLEDs) with heavy metals or TADF materials are regularly reported due to the advantages of their various applications in healthcare services, veil authentication, and night vision displays. In this paper, we are summarized the collection of innovative organic near‐infrared (NIR) emitters which is crucial factor to design specific NIR emitter for NIR OLEDs [ABSTRACT FROM AUTHOR]

Thermally activated delayed fluorescence (TADF) and long persistent luminescence (LPL) are emerging photophysical hotspots, which involve the singlet/triplet excited states and two‐way energy transfer processes between them via intersystem crossing (ISC) or reverse intersystem crossing (RISC). Herein, a new tactic is reported for the regulation of keto‐energy levels and ISC/RISC equilibrium via the introduction of electron‐withdrawing fluorine in a series of excited state intramolecular proton transfer (ESIPT) ligands and corresponding Cd(II) coordination polymers. Among them, the fluorine p‐substituted to the hydroxy group along the nodal plane on the phenol site improves the thermodynamic stability of the keto‐isomers of the ligand, thereby lowering the keto‐energy level and promoting the ESIPT process effectively. Uniquely, the lower‐energy keto excited state makes the ISC/RISC equilibrium shift to the direction of RISC progress, and thus arousing efficient TADF in the constructed coordination polymer. A comprehensive transient photophysical and theoretical study verifies the greatly promoted RISC progress, rather than suppressed ISC is aroused in the p‐substituted system, suggesting a clear‐cut strategy in the design of coordination polymers with good TADF performance. [ABSTRACT FROM AUTHOR]

Constructing an ultra‐long‐lived red thermally activated delayed fluorescence carbon dots (TADF‐CDs) with time‐dependent phosphorescence colors (TDPC) in both solid and aqueous is still a challenge. Herein, a red TADF‐CDs, constructed via. a modified solid‐state pyrolysis strategy, show the phosphorescence emissions at 595, 670, and 725 nm with the afterglow lifetime longer than most of reported red TADF‐materials. In addition, the resulting CDs trigger the TDPC activity while the emission colors changed from red to green both in solid state and in aqueous suspension. The synergistic effects of boron‐hybridization in the seed CDs and the additional C═O groups generated in urea‐assisted pyrolysis, result in a stronger spin‐orbit coupling (SOC) between the 1(n, π*) and the 3(π, π*), the mitigated energy gap (ΔEST) and the non‐radiative relaxations of triplet excited states. The TDPC performance endow the resulting TADF‐CDs the usability in advance information security with enhanced‐security‐level encryption strategy. [ABSTRACT FROM AUTHOR]

This study conducts a thorough theoretical investigation of Thermally Activated Delayed Fluorescence (TADF) in phenothiazine‐based systems, examining ten molecular configurations recognized experimentally as TADF‐active. Employing Time‐Dependent Density Functional Theory (TD‐DFT), our analysis spans the investigation of singlet‐triplet energy gaps (ΔEST), spin‐orbit coupling, and excitation characteristics using Multiwfn. This approach not only validates the adherence to El Sayed's rule across these systems but also provides a detailed understanding of charge transfer dynamics, as visualized through heat maps. A significant aspect of our study is the exploration of different oxidation states of sulfur and site substitutions on phenothiazine. This systematic variation aims to identify additional TADF‐active compounds, drawing parallels with properties characterizing other known TADF emitters. Our investigation into Reverse Intersystem Crossing (rISC) rates and the analysis of dihedral angles in relation to ΔEST values offer nuanced insights into the TADF behaviours of these molecules. By integrating rigorous computational analysis with practical implications, we provide a foundational understanding that enhances the design and optimization of phenothiazine‐based materials for optoelectronic applications. This work not only advances our theoretical understanding of TADF in phenothiazine derivatives but also serves as a guide for experimentalists and industry professionals in the strategic design of new TADF materials. [ABSTRACT FROM AUTHOR]

Helical nanographenes have garnered substantial attention owing to their finely adjustable optical and semiconducting properties. The strategic integration of both helicity and heteroatoms into the nanographene structure, facilitated by a boron‐oxygen‐based multiple resonance (MR) thermally activated delayed fluorescence (TADF), elevates its photophysical and chiroptical features. This signifies the introduction of an elegant category of helical nanographene that combines optical (TADF) and chiroptical (CPL) features. In this direction, we report the synthesis, optical, and chiroptical properties of boron, oxygen‐doped Π‐extended helical nanographene. The π‐extension induces distortion in the DOBNA‐incorporated nanographene, endowing a pair of helicenes, (P)‐B2NG, and (M)‐B2NG exhibiting circularly polarized luminescence with glum of −2.3×10−3 and +2.5×10−3, respectively. B2NG exhibited MR‐TADF with a lifetime below 5 μs, and a reasonably high fluorescence quantum yield (50 %). Our molecular design enriches the optical and chiroptical properties of nanographenes and opens up new opportunities in multidisciplinary fields. [ABSTRACT FROM AUTHOR]

Thermally activated delayed fluorescent (TADF) emitters attract interest as organic light‐emitting diode (OLED) materials with potentially 100% internal quantum efficiency (IQE). Their application in commercial displays is still hindered due to the not yet sufficient operational stability. We analyze the degradation mechanism in a TADF OLED by combining electro‐optical characterization and device simulations. We find that two trap states are being created at the HTL/EML interface during initial degradation. [ABSTRACT FROM AUTHOR]

Thermally activated delayed fluorescence (TADF) materials have numerous applications in energy conversion and luminescent imaging. However, they are typically achieved as metal‐organic complexes or pure organic molecules. Herein, we report the largest Au‐Ag‐oxo nanoclusters to date, Au18Ag26(R1COO)12(R2C≡C)24(μ4‐O)2(μ3‐O)2 (Au18Ag26, where R1 = CH3‐, Ph‐, CHOPh‐ or CF3Ph‐; R2 = Ph‐ or FPh‐). These nanoclusters exhibit exceptional TADF properties, including a small S1‐T1 energy gap of 55.5 meV, a high absolute photoluminescence quantum yield of 86.7%, and a microseconds TADF decay time of 1.6 μs at ambient temperature. Meanwhile, Au18Ag26 shows outstanding stability against oxygen quenching and ambient conditions. Atomic level analysis reveals the strong π⋯π and C‐H⋯π interactions from the aromatic alkynyl ligands and the enhancement of metal‐oxygen‐metal interactions by centrally coordinated O2−. Modeling of the electronic structure shows spatially separated highest occupied molecular orbital and lowest unoccupied molecular orbital, which promote charge transfer from the ligand shell, predominantly carboxylate ligands, to O2−‐embedded metal core. Furthermore, TADF Au‐Ag‐oxo nanoclusters exhibit promising radioluminescence properties, which we demonstrate for X‐ray imaging. Our work paves the way for the design of TADF materials based on large metal nanoclusters for light‐emission and radioluminescence applications. [ABSTRACT FROM AUTHOR]

Long-lived thermally activated delayed fluorescence (TADF) emission has gained extensive attention due to its potential application in information encryption, illumination, and bioimaging. However, developing visible light-excited TADF materials is still a significant challenge. Herein, visible light triggered TADF emission was achieved by embedding chlorine doped carbon dots (Cl-CDs) into a g-C3N4 nanosheet matrix through a simple microwave treatment. The strong electron-withdrawing effect of the chlorine dropping redshifts the excitation wavelength, and the covalent bonds between Cl-CDs and the matrix significantly stabilize the triplet state. Green TADF with a peak at 520 nm could be obtained in the Cl-CD composite when excited by the UV to visible light, and the afterglow signal can be observed by the naked eye for up to 5 s after a mobile phone flashlight irradiation. The composite also exhibited temperature-responsive color stability under UV light irradiation. Consequently, the Cl-CD composite was successfully employed in concepts of information encryption and single-component time delay WLED development. This research provides materials and strategies that may motivate the visible light-excited TADF applied in advanced information encryption and illumination areas. [ABSTRACT FROM AUTHOR]

A novel class of o‐carboranyl luminophores, 2CB‐BuDABNA (1) and 3CB‐BuDABNA (2) is reported, in which o‐carborane moieties are incorporated at the periphery of the B,N‐doped multi‐resonance thermally activated delayed fluorescence (MR‐TADF) core. Both compounds maintain the inherent local emission characteristics of their MR‐emitting core, exhibiting intense MR‐TADF with high photoluminescence quantum yields in toluene and rigid states. In contrast, the presence of the dark lowest‐energy charge transfer state, induced by cage rotation in THF, is suggested to be responsible for emission quenching in a polar solvent. Despite the different arrangement of the cage on the DABNA core, both 1 and 2 show red‐shifted emissions compared to the parent compound BuDABNA (3). By utilizing 1 as the emitter, high‐efficiency blue organic light‐emitting diodes (OLEDs) are achieved with a remarkable maximum external quantum efficiency of 25%, representing the highest reported efficiency for OLEDs employing an o‐carboranyl luminophore as the emitter. [ABSTRACT FROM AUTHOR]

Two derivatives of phenyl pyrimidine as acceptor unit and triphenylamino or 4,4′-dimethoxytriphenylamino donor groups were designed and synthesized as emitters for organic light-emitting diodes (OLEDs) aiming to utilize triplet excitons in the electroluminescence. Thermogravimetric analysis revealed high thermal stability of the compounds with 5% weight loss temperatures of 397 and 438 °C. The theoretical estimations and photophysical data show the contributions of local excited and charge transfer states into emission. The addition of the methoxy groups led to the significant improvement of hole-transporting properties and the bathochromic shift of the emission from blue to green-blue spectral diapason. It is shown that mixing of the compounds with the organic host results in facilitation of the delayed emission. The singlet–triplet energy splitting was found to be too big for the thermally activated delayed fluorescence. No thermal activation of the long-lived emission was detected. No experimental evidence for triplet–triplet annihilation and room temperature phosphorescence were detected making the hot exciton mechanism the most probable one. The OLEDs based on the compounds reached the maximum external quantum efficiency of up to 10.6%. [ABSTRACT FROM AUTHOR]

Third-generation organic light-emitting diodes (OLEDs) based on metal-free thermally activated delayed fluorescent (TADF) materials have sparked tremendous interest in the last decade due to their nearly 100% exciton utilization efficiency, which can address the low-efficiency issue of the first-generation fluorescent emitters and the high-cost issue of the second-generation organometallic phosphorescent emitters. Construction of efficient and stable TADF-OLEDs requires utilizing TADF materials with a narrow singlet–triplet energy gap (ΔEST), high photoluminescence quantum yield (PLQY) and short TADF lifetime. A small ΔEST is necessary for an efficient reverse intersystem crossing (RISC) process, which can be achieved through the effective spatial separation of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO). TADF emitters have been generally designed as intramolecular charge transfer (ICT) molecules with highly twisted donor–acceptor (D–A) molecular architectures. A wide variety of combinations of electron donors and acceptors have been explored. In this review, we shall focus on recent progress in organic TADF molecules incorporating strong electron-donor phenoxazine moiety and their application as emitting layer (EML) in OLEDs. [ABSTRACT FROM AUTHOR]

The design and synthesis of four twisted donor‐acceptor (D‐A) thermally activated delayed fluorescence (TADF) molecules CBZ‐IQ, CBZ‐2FIQ, DI‐IQ and DI‐2FIQ is reported in this work based on diindolocarbazole (DI) and phenyl carbazole as donor and indoloquinoxalines as acceptor. These compounds serve as photocatalysts for organic transformations. Theoretical calculations and experimental data showed reasonable singlet and triplet energy gaps of 0.17‐0.26 eV for all compounds. All molecules showed increase in fluorescence quantum yields after degassing the solution and the transient photoluminescence decay showed two components: shorter prompt components (11.4 ns to 31 ns) and longer delayed components (36.4 ns to 1.5 μs) which further indicate the occurrence of TADF process. Cyclic voltammetry studies indicated well‐suited excited state redox potentials of all compounds to catalyze organic transformations such as heteroarene arylation. Accordingly, photocatalytic C−H arylation of heteroarenes were performed using these compounds with excellent isolated yields of upto 80 %. Due to their suitable efficient triplet energy levels, all the emitters were also employed as energy transfer photocatalysts in E to Z isomerization of stilbene with the excellent conversion of ~90 %. [ABSTRACT FROM AUTHOR]

Living system involves a plenty of delicate processes where a tiny structural variation of biological substance may lead to drastic change of the fate of the living system. Inspired by this, in artificial photofunctional systems, if tiny structural variation changes the fate of excited states, a new class of advanced material would emerge for optical analysis, sensing, and next‐generation display is reasoned. However, such delicate processes remain rarely explored in photofunctional systems, especially in room temperature organic afterglow systems. Here the attachment/detachment of methoxy group can switch off/on twisted intramolecular charge transfer property in difluoroboron β‐diketonate systems is reported. In addition, structural isomerization triggers afterglow transformation from room temperature phosphorescence to thermally activated delayed fluorescence. These observations are helpful for better photophysical understanding on luminescence systems and advanced material design. [ABSTRACT FROM AUTHOR]

Luminescent metal complexes based on earth abundant elements are a valuable target to substitute 4d/5d transition metal complexes as triplet emitters in advanced photonic applications. Whereas CuI complexes have been thoroughly investigated in the last two decades for this purpose, no structure‐property‐relationships for efficient luminescence involving triplet excited states from ZnII complexes are established. Herein, we report on the design of monomeric carbene zinc(II) dithiolates (CZT) featuring a donor‐acceptor‐motif that leads to highly efficient thermally activated delayed fluorescence (TADF) with for ZnII compounds unprecedented radiative rate constants kTADF=1.2×106 s−1 at 297 K. Our high‐level DFT/MRCI calculations revealed that the relative orientation of the ligands involved in the ligand‐to‐ligand charge transfer (1/3LLCT) states is paramount to control the TADF process. Specifically, a dihedral angle of 36–40° leads to very efficient reverse intersystem‐crossing (rISC) on the order of 109 s−1 due to spin‐orbit coupling (SOC) mediated by the sulfur atoms in combination with a small ΔES1‐T1 of ca. 56 meV. [ABSTRACT FROM AUTHOR]

This study proposes a novel approach to develop highly efficient, narrow‐emitting violet materials based on boron and oxygen polycyclic aromatic hydrocarbon multiple resonance structure. Herein, B‐2OCz is developed by fusing indole with a 5,9‐dioxa‐13bboranaphtho[3,2,1‐de]anthracene (DOBNA) core to enhance its thermally activated delayed fluorescence (TADF) properties and molecular rigidity. On the other hand, the B‐2OCz‐Si is decorated with a bulky tetraphenylsilyl substituent. B‐2OCz‐Si exhibits exceptional features such as violet emission at 397 nm, a very small full width at half maximum of 16 nm, and 82% of photoluminescence quantum yield. The B‐2OCz‐Si devices achieve a high external quantum efficiency of over 15%, violet emission with a peak wavelength of 423 nm, and color coordinates of (0.156, 0.037). Furthermore, the B‐2OCz‐Si is used as an electron transport type host material for phosphorescent organic light‐emitting diodes (PhOLEDs), based on its high triplet energy and TADF properties. As compared to the conventional triazine based host materials, these newly developed DOBNA‐based materials display superior device lifetime performance. All these potential aspects corroborate that this new class of DOBNA‐based materials can work as a promising host material for PhOLEDs and violet‐emitting fluorescent devices. [ABSTRACT FROM AUTHOR]

This research focuses on a theoretical study of diphenylsulfone-based emitters for thermally activated delayed fluorescence (TADF). The acceptor moiety employed in this study is sulfonyldibenzene, while the donor moiety is 9H-carbazole. The effects of methoxy, thiophene, pyridine, and pyrazine adding on the donor moiety were investigated, resulting in the design of six distinct molecules. Density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods, utilizing the B3LYP functional with 6-311G(d,p) basis sets, were used to assess the properties of these compounds in their singlet, doublet, and triplet states. The calculations encompassed various aspects, including ground state molecular geometry, electronic properties, dipole moments, polarizabilities, frontier orbital energies, density of states, UV-Vis spectra, and IR spectra. The investigation revealed that adding the donor moiety with rings, particularly thiophene and pyridine, resulted in improved properties, including molecular geometry. Furthermore, increasing the D-A dihedral angle was found to increase the energy gap, optical gap, dipole moments, and polarizabilities, while reducing the ∆EST and the overlap between the HOMO and LUMO. Hole-electron analysis demonstrated that all the compounds exhibited localized excitation characteristics, with the electrons being photoinduced locally. These compounds exhibited strong blue emissions, with maximum wavelengths ranging from 387.462 to 458.286 nm in the singlet-triplet states. Moreover, the designed compounds exhibited coverage of the entire visible region in their UV-Vis spectra when in the doublet state. Based on these findings, these compounds show promise as TADF emitters in organic light-emitting diodes (OLEDs), providing improvements in efficiency and properties. [ABSTRACT FROM AUTHOR]