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This study presents the design, synthesis, and comprehensive theoretical and photophysical analysis of two new D 3 -A type thermally activated delayed fluorescence (TADF) emitters for organic light-emitting diode (OLED) applications. Utilizing a triarylboron core as the electron-accepting group and phenothiazine (PTZ) or phenoselenazine (PSZ) as electron-donating units, the molecules BTP-S and BTP-Se were developed. The D 3 -A structure supports the separation of frontier molecular orbitals (FMOs), leading to minimized singlet-triplet energy gaps (ΔE ST), which are crucial for the TADF mechanism. Density functional theory (DFT) calculations presented that BTP-S and BTP-Se exhibit band gaps (E g) of 2.52 and 3.23 eV, respectively, with BTP-S showing an ΔE ST value as low as 0.007 eV for the S 1 -T 1 transition at the lowest energy conformation. Photophysical studies revealed high photoluminescence quantum yields (PLQYs) for both compounds, with BTP-S achieving up to 85 % in mCP films and BTP-Se up to 59 %. In vacuum-processed OLEDs, BTP-S achieved a maximum external quantum efficiency (EQE) of 25.3 %, a current efficiency (ηc) of 195.8 cd/A, and a maximum luminance (Lmax) of 17356 cd/m2, while BTP-Se reached an EQE of 7.5 %, an ηc of 132.19 cd/A, and an Lmax of 16826 cd/m2 likely limited by the contributions of a folded-donor conformer enabled by the Se substitution. These findings underscore the impact of donor unit selection and conformation on the TADF characteristics, and provide valuable insights for designing high-performance OLED materials. [Display omitted] • Two novel D3-A type TADF emitters, BTP-S and BTP-Se, were designed and synthesized. • Both theoretical and photophysical results are consistent with a thermally activated mechanism of delayed fluorescence. • High photoluminescence quantum yields: BTP-S up to 85 %, BTP-Se up to 59 % in mCP films. • BTP-Se reached EQE of 7.5 %, ηc of 132.19 cd/A, and Lmax of 16826 cd/m2. • BTP-S achieved EQE of 25.3 %, ηc of 195.8 cd/A, and L max of 17356 cd/m2. [ABSTRACT FROM AUTHOR]

The effects of the solvent used for the active layer materials of an OLED based on TADF emitters play a fundamental role in solution-deposited devices. This work focuses on the effects on the performance of different solvents employed to fabricate a very simple two-organic-layer OLED based on a green TADF emitter, under the concept of host: guest matrix. From the different results of the main figures of merit, it was possible to conclude that the OLED that used toluene as a solvent for the active layer reached a maximum EQE of 14%, almost the maximum already obtained for this emitter in more complex device structures. With the analysis of the charge-transport processes, it was possible to establish an explanatory model for the obtained results. Through impedance spectroscopy, additional characterization of the nature of charge-transport processes was carried out. With these results, it was possible to correlate the relaxation times, with the electrical properties of the active layer, and make inferences about the interaction between the electrical charges and the defect levels, opening new possibilities for further development in printed OLEDs.

Interface exciplex represents a promising host material for organic light‐emitting diodes (OLEDs) with barrier‐free charge injection and highly confined recombination region. However, the efficiency of radiative recombination in pristine exciplex is usually low and needs to be improved by doping various emitters. In this study, the interface exciplex OLEDs doped with fluorescence, phosphorescence, and thermally activated delayed fluorescence (TADF) emitters is fabricated to investigate the relationship between their excited‐state properties and electroluminescence efficiencies. A maximum external quantum efficiency of 20% is achieved in interface exciplex OLEDs doped with TADF emitter, which corresponds to nearly 100% exciton utilization and is superior to those of fluorescence and phosphorescence emitters. Furthermore, optical spectroscopy and magneto‐electroluminescence method are used to study the advantages of TADF emitter in interface exciplex host. The large dipole of TADF emitter is beneficial for harvesting energy from the charge‐transfer state at the interface, and its reverse intersystem crossing avoids the accumulation of triplet excitons that leads to triplet‐triplet annihilation in interface exciplex OLEDs. These results demonstrate that the photophysical process needs to be carefully considered in designing high‐performance emitters for exciplex host materials, and it may bring in‐depth understanding on improving exciton utilization and electroluminescence efficiency in interface exciplex OLEDs. [ABSTRACT FROM AUTHOR]

In the search for solution-processable TADF materials as a light emitting layer for OLED devices, polymers have attracted considerable attention due to their better thermal and morphological properties in the film state with respect to small molecules. In this work, a new polymer (p-TPS-DMAC-TRZ) with thermally activated delayed fluorescence (TADF) light-emitting characteristics was prepared from a conjugation-break unit (TPS) and a well-known TADF core (DAMC-TRZ). This material was designed to preserve the photophysical properties of DAMC-TRZ, while improving other properties, such as thermal stability, promoted by its polymerization with a TPS core. Along with excellent solubility in common organic solvents such as toluene, chloroform and THF, the polymer (Mn = 9500; Mw = 15200) showed high thermal stability (TDT5% = 481 °C), and a Tg value of 265 °C, parameters higher than the reference small molecule DMAC-TRZ (TDT5% = 305 °C; Tg = 91 °C). The photoluminescence maximum of the polymer was centered at 508 nm in the solid state, showing a low redshift compared to DMAC-TRZ (500 nm), while also showing a redshift in solution with solvents of increasing polarity. Time-resolved photoluminescence of p-TPS-DMAC-TRZ at 298 K, showed considerable delayed emission in solid state, with two relatively long lifetimes, 0.290 s (0.14) and 2.06 s (0.50), and a short lifetime of 23.6 ns, while at 77 K, the delayed emission was considerably quenched, and two lifetimes in total were observed, 24.6 ns (0.80) and 180 ns (0.20), which was expected from the slower RISC process at lower temperatures, decreasing the efficiency of the delayed emission and demonstrating that p-TPS-DMAC-TRZ has a TADF emission. This is in agreement with room temperature TRPL measurements in solution, where a decrease in both lifetime and delayed contribution to total photoluminescence was observed when oxygen was present. The PLQY of the mCP blend films with 1% p-TPS-DMAC-DMAC-TRZ as a dopant was determined to be equal to 0.62, while in the pure film, it was equal to 0.29, which is lower than that observed for DMAC-TRZ (0.81). Cyclic voltammetry experiments showed similarities between p-TPS-DMAC-TRZ and DAMC-TRZ with HOMO and LUMO energies of −5.14 eV and −2.76 eV, respectively, establishing an electrochemical bandgap value of 2.38 eV. The thin film morphology of p-TPS-DMAC-TRZ and DMAC-TRZ was compared by AFM and FE-SEM, and the results showed that p-TPS-DMAC-TRZ has a smoother surface with fewer defects, such as aggregations. These results show that the design strategy succeeded in improving the thermal and morphological properties in the polymeric material compared to the reference small molecule, while the photophysical properties were mostly maintained, except for the PLQY determined in the pure films. Still, these results show that p-TPS-DMAC-TRZ is a good candidate for use as a light-emitting layer in OLED devices, especially when used as a host-guest mixture in suitable materials such as mCP. [ABSTRACT FROM AUTHOR]

Narrowband deep blue thermally activated delayed fluorescent (TADF) materials have attracted significant attention. Herein, four asymmetrical structured TADF emitters based on diphenylsulfone (DPS) acceptor and 9,9‐dimethyl‐9,10‐dihydroacridine (DMAC) donor with progressive performances were developed. The tert‐butyloxy auxiliary electron‐donor was adopted to restrict the intramolecular rotations and provide efficient steric hindrance. Regioisomerization by altering the substitution position of DMAC on DPS unit further enhanced the intra‐ and inter‐molecular interactions. The accompanying effects yielded increased energy level, minimized reorganization energy, and inhibited non‐radiative transitions in the crystals of tBuO‐SOmAD, which achieved narrowband deep‐blue emission peaking at 424 nm (FWHM=64 nm, ΦF=33.6 %) through aggregation‐induced, blue‐shifted emission (AIBSE). In addition, deep‐blue organic light emitting diodes (OLEDs) based on tBuO‐SOmAD realized the electroluminescence (EL) spectrum peaking located at 435 nm and CIE coordination of (0.12, 0.09). [ABSTRACT FROM AUTHOR]

The harnessing of heavy atom effect of chalcogen elements offers a way for boosting the thermally activated delayed fluorescence (TADF) of purely organic luminescent materials that can harvest triplet excitons. However, the conformational and electronic variations induced by the heavy and large atoms may also have adverse effects on the TADF properties. Herein, the design, synthesis, and structures of a new type of through‐space charge transfer (TSCT) emitters containing benzothiazino[2,3,4‐kl]phenothiazine (DPTZ) as the donor unit are reported. The influences of S atoms on the emission properties have been systematically investigated by means of theoretical simulations, electrochemical and spectroscopic studies. Although the presence of π‐stacking interactions and calculated spin‐orbit coupling (SOC) values are beneficial for TSCT‐TADF properties, the triplet TSCT states are uplifted to above the locally excited (LE) state of the acceptor moieties. As a result, the new emitters display longer delayed fluorescence lifetimes (τDF) of 255.0–114.3 μs and lower PLQYs of 45–61 % in comparison with the O‐containing congeners (τDF=26.9–6.8 μs; PLQYs=74–71 %). This work highlights that a full consideration of various effects is essential when making use of heavy chalcogen atoms for the design of TADF emitters. [ABSTRACT FROM AUTHOR]

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

Observation of thermally activated delayed fluorescence (TADF) in conjugated systems redefined the molecular design approach to realize highly efficient organic light emitting diodes (OLEDs) in the early 2010s. Enabling effective reverse intersystem crossing (RISC) by minimizing the difference between singlet and triplet excited state energies (ΔEST) is proven to be a widely applicable and fruitful approach, which results in remarkable external quantum efficiencies (EQE). The efficacy of RISC in these systems is mainly dictated by the first‐order mixing coefficient (λ), which is proportional to spin‐orbit coupling (HSO) and inversely proportional to ΔEST. While minimizing ΔEST has been the focus of the OLED community over the last decade, the effect of HSO in these systems is largely overlooked. Here, molecular systems with increased HSO are designed and synthesized by substituting selected heteroatoms of high‐performance TADF materials with heavy‐atom selenium. A new series of multicolor TADF materials with remarkable EQEs are achieved. One of these materials, SeDF‐B, results in pure blue emission with EQEs approaching 20%. Additionally, flexible graphene‐based electrodes are developed for OLEDs and revealed to have similar performance as standard indium tin oxide (ITO) in most cases. These devices are the first report of TADF based OLEDs that utilize graphene‐based anodes. [ABSTRACT FROM AUTHOR]

The scalable synthesis of figure-eight π-systems is challenging for the conventional bottom-up approach. We have recently reported that the oxidative inner-bond cleavage of commercially available dibenzo[g,p]chrysene efficiently furnishes a figure-eight π-acceptor, cyclobisbiphenylenecarbonyl (CBBC), in large quantity. Furthermore, its donor-acceptor-type derivative with four N-carbazolyl substituents at the meta-positions of the carbonyl groups exhibited thermally activated delayed fluorescence (TADF) and circularly polarized luminescence (CPL) with a high |gCPL| value of 1.0 × 10-2. Herein, we synthesized nine donor-acceptor-type CBBC derivatives by changing the donor substituents and their positions. Compared to previously reported carbazole-substituted CBBC, tetramethylcarbazole- and 9,10-dihydro-9,9-dimethylacridine-substituted derivatives exhibited enhanced emission quantum yields and accelerated reverse intersystem crossing. The functionalization of the para-positions of the carbonyl groups resulted in better tunability of emission colors rather than meta-functionalization, whose color variation ranges from light blue to red. The incorporation of bulky substituents at the meta-positions of the carbonyl groups induced the conformational change to a distorted ring structure. Investigation of the substituent effect on the chiroptical properties revealed that the introduction of less bulky donor units such as carbazole at the meta-positions of the carbonyl groups is effective in achieving high |gCPL| values., (© 2024 Wiley‐VCH GmbH.)

It holds enormous significance for red thermally activated delayed fluorescence (TADF) emitters to develop organic light-emitting diodes (OLEDs) with high efficiency and high color purity, which remains challenging for highly efficient solution-processed red TADF emitters due to the limitation of severe nonradiative decays. Herein, a red TADF emitter containing space interactions, 4,4'-(9,10-bis(phenylethynyl)anthracene-1,8-diyl)bis( N , N -bis(4-methoxyphenyl)aniline) (DBP-2MOTPA), is designed and synthesized, composed of ethynyl as the acceptor and methoxytriarylamine (MOTPA) as the donor. The triphenylamine donor unit decorated with peripheral methoxy units not only improves the solubility for the solution-processed technology but also increases the electron-donating ability. The highly twisted donor-π-acceptor (D-π-A) architecture generates a small energy gap (Δ E ST ) of 68%. Consequently, the nondoped device based on DBP-2MOTPA with Commission Internationale de l'Eclairage (CIE) at (0.67, 0.33) exhibits the pure red emission, which satisfies the Rec.1931 standard red gamut (0.67, 0.33) and approaches the Rec.2020 standard (0.71, 0.29). Moreover, the doped devices employing DBP-2MOTPA as the emitter exhibit a maximum external quantum efficiency (EQE) of 6.09%, which is among the effective values in the solution-processed red TADF-OLEDs.PL ) of 68%. Consequently, the nondoped device based on DBP-2MOTPA with Commission Internationale de l'Eclairage (CIE) at (0.67, 0.33) exhibits the pure red emission, which satisfies the Rec.1931 standard red gamut (0.67, 0.33) and approaches the Rec.2020 standard (0.71, 0.29). Moreover, the doped devices employing DBP-2MOTPA as the emitter exhibit a maximum external quantum efficiency (EQE) of 6.09%, which is among the effective values in the solution-processed red TADF-OLEDs.

In this study, HATCN is coated on flexible PET/indium tin oxide (ITO) substrate as a modified layer and a hole injection layer to improve the hole injection from ITO. Then a blue organic light emitting diode (OLED) can successfully be fabricated without a surface treatment procedure (O2 plasma or UV Ozone treatment). The new blue TADF series fluorescent material is employed as emitting layer with a luminescence wavelength of 456 nm. Also, it has a narrow full width at a half maximum (FWHM) of 26 nm featuring excellent color chromaticity. Quantum dot (QD) photoresist is a perfect color conversion material featuring good color adjustability, narrow emission spectrum, high luminous efficiency, and simple spin-coating processes. In this study, the photoresist mixed with green and red quantum dots is used as a color conversion layer (CCL), and a blue OLED is utilized to excite green and red CCL. To test the material of QD photoresist, it is coated on the substrate of another piece of glass first and then the blue OLED is utilized to remotely excite green and red QD CCL. The fluorescence characteristic of QD photoresist is explored to acquire a spectrum of 528 nm and 620 nm. In the device structure of a blue OLED, the electron-and hole-only current density is compared and the hole transport layer TAPC thickness is adjusted to improve the luminance and efficiency. Finally, green and red quantum dot photoresist is mixed using a proper ratio and then directly coated on the back of the PET/ITO substrate. Furthermore, the thickness of the QD photoresist is adjusted to increase the QD excited fluorescence. The blue OLED and QD CCL was integrated to generate three primary colors, i.e., blue, green, and red. Finally, a flexible white OLED lighting panel is successfully fabricated using simple processes. Moreover, it features high-spectrum stability. The CIE coordinates will not drift with bias, thus, it can resist the voltage variation.

Abstract Thermally activated delayed fluorescence (TADF)-sensitized fluorescence is a promising strategy to maintain the advantage of TADF materials and fluorescent materials. Nevertheless, the delayed lifetime of the TADF sensitizer is still relatively long, which causes heavy efficiency roll-off. Here we reported a valid tactic to construct fluorescent devices with low-efficiency roll-off by utilizing the TADF sensitizer with a reduced delayed lifetime. By the construction of the sensitization system, the energy transfer efficiency can reach up to 90%. The high-energy transfer efficiency and the TADFʼs short delayed lifetime result in high sensitization over 95% and the maximum external quantum efficiency of 16.2%. Meanwhile, the TADF-sensitized fluorescent devices exhibit reduced efficiency roll-off with an “onset” current density of 23 mA · cm−2. Our results provide an effective strategy to reduce the efficiency roll-off of the TADF sensitization system.

Abstract All-organic thermally activated delayed fluorescence (TADF) materials have emerged as potential candidates for optoelectronic devices and biomedical applications. However, the development of organic TADF probes with strong emission in the longer wavelength region (> 600 nm) remains a challenge. Strong π-conjugated rigid acceptor cores substituted with multiple donor units can be a viable design strategy to obtain red TADF probes. Herein, 3,6-di-t-butyl carbazole substituted to a dibenzopyridoquinoxaline acceptor core resulted in a T-shaped donor–acceptor–donor compound, PQACz-T, exhibiting red TADF in polymer-embedded thin-films. Further, PQACz-T self-assembled to molecular nanoaggregates of diverse size and shape in THF–water mixture showing bright red emission along with delayed fluorescence even in an aqueous environment. The self-assembly and the excited-state properties of PQACz-T were compared with the nonalkylated analogue, PQCz-T. The delayed fluorescence in nanoaggregates was attributed to the high rate of reverse intersystem crossing. Moreover, an aqueous dispersion of the smaller-sized, homogeneous distribution of fluorescent nanoparticles was fabricated upon encapsulating PQACz-T in a triblock copolymer, F-127. Cytocompatible polymer-encapsulated PQACz-T nanoparticles with large Stokes shift and excellent photostability were demonstrated for the specific imaging of lipid droplets in HeLa cells.

Thermally activated delayed fluorescence (TADF) molecules have a theoretical 100% photoluminescence quantum yield in comparison with traditional fluorescent materials, leading to broad application in organic light-emitting diode (OLED). However, the application of TADF molecules with conjugated donor-acceptor structures in blue OLED remains a challenge due to their generally narrow energy gap between frontier molecular orbitals. Recently, a strategy has been approved in the improvement of the performance in TADF, in which void-carbon atoms between donor and acceptor fragments (donor-void-acceptor (D-v-A)) could regulate blue light emission. In this study, we first select three reported isomers followed by two proposed D-v-A TADF isomers to verify the feasibility of the void-carbon strategy through evaluation of the electronic structures in the excited state and photophysical properties. We further proposed a series of TADF molecules by replacing different donor and acceptor fragments to assess the applicability of the void-carbon strategy from the aspect of simulations in electronic structures, different properties of donor and acceptor fragments, photophysical properties, and analysis in the molecular conjugation. The results indicate that void-carbon strategy has conditional feasibility and applicability. Donor-acceptor molecular properties could be tuned through void-carbon strategy on aromatic acceptor fragments during the selection of promising candidates of TADF molecules. However, the void-carbon strategy does not work for the molecules with antiaromatic acceptor fragments, where the steric hindrance of the molecules plays a dominant role. Our work provides insightful guidance for the design of the blue-emission TADF molecules.

The practical use of luminescent mononuclear gold(I) complexes as optoelectronic materials has been limited by their inferior stability. Herein we demonstrate a strategy to improve the stability of gold(I) complexes which display thermally activated delayed fluorescence (TADF). A highly rigid and groove‐like σ‐donating aryl ligand has been used to form dual Au⋅⋅⋅H−C hydrogen bonds. The secondary metal‐ligand interactions have been authenticated by single‐crystal structure, NMR spectroscopy and theoretical simulations. The TADF AuI complex exhibits appealing emission properties (photoluminescence quantum yield=76 %; delayed fluorescence lifetime=1.2 μs) and much improved thermal and photo‐stability. Vacuum‐deposited organic light‐emitting diodes (OLEDs) show promising electroluminescence with a maximum external quantum efficiency (EQE) over 23 % and negligible efficiency roll‐off even at 10 000 cd m−2. An estimated LT50 longer than 77 000 h with initial luminance of 100 cd m−2 reveals good operational stability. This work suggests a way for design of stable luminescent gold(I) complexes. [ABSTRACT FROM AUTHOR]

There is increasing interest in thermally activated delayed fluorescence (TADF) in materials, and to understand its mechanism in the excited state dynamics. Recent challenges include color purity, efficient deep‐blue emission, fast exciton decay lifetimes, high reverse intersystem crossing rates (kRISC), low‐efficiency roll‐off in organic light‐emitting diodes (OLEDs), and long device lifetimes. Here, a series of compounds having benzonitrile and carbazole rings are examined, that provide a detailed understanding of the excited states, and a guideline for high‐performance TADF. A dense alignment of the excited states with several different characters within a small energy range results in high kRISC of >2 × 106 s−1, while maintaining radiative rate constants (kr) >107 s−1. OLEDs based on the optimum compound exhibit a low‐efficiency roll‐off and a CIEy (y color coordinate of Commission Internationale de l'Éclairage) <0.4. TADF‐assisted fluorescence (TAF) OLED exhibits a maximum external quantum efficiency of 22.4% with CIE coordinates (0.13,0.15). This work also provides insights for device engineering and molecular designs. [ABSTRACT FROM AUTHOR]

The electronic and structural alterations induced by the functionalization of the 1,10-phenanthroline (phen) ligand in [Cu(I) (phen-R2)2]+ complexes (R=H, CH3, tertio-butyl, alkyl-linkers) and their consequences on the luminescence properties and thermally activated delay fluorescence (TADF) activity are investigated using the density functional theory (DFT) and its time-dependent (TD) extension. It is shown that highly symmetric molecules with several potentially emissive nearly-degenerate conformers are not promising because of low S1/S0 oscillator strengths together with limited or no S1/T1 spin–orbit coupling (SOC). Furthermore, steric hindrance, which prevents the flattening of the complex upon irradiation, is a factor of instability. Alternatively, linking the phenanthroline ligands offers the possibility to block the flattening while maintaining remarkable photophysical properties. We propose here two promising complexes, with appropriate symmetry and enough rigidity to warrant stability in standard solvents. This original study paves the way for the supramolecular design of new emissive devices. [ABSTRACT FROM AUTHOR]

Previous work has reported the synthesis of donor–acceptor–donor molecules based on dibenzophenazine acceptor group, presenting thermally activated delayed fluorescent (TADF) properties and their application in the assembly of highly efficient electroluminescent devices. Herein, we focus on the characterisation of charge carrier species through UV‐Vis‐NIR spectroelectrochemical and potentiostatic EPR techniques, in addition to the investigation of electropolymerisation properties of some compounds depicted in this study. The promising electrochromic features of both small molecules and conjugated polymers led to the assembly and investigation of electrochromic devices, evidencing the materials' versatility, applied in such different approaches as electrochromic windows and electroluminescent devices. Furthermore, the assembled OLEDs provided high efficiencies, with small roll‐off, EQEs up to 20.5 % and luminance values up to 85 000 cd/m2. [ABSTRACT FROM AUTHOR]

Organic light-emitting diodes have great potential to meet the future demand of low-energy lighting and display products. In the present work, we have studied the effect of using a phosphorescent and a thermally activated delayed fluorescence (TADF) guest emissive material with the same host blend, on the emissive thin film properties. In order to get superior hole as well as electron mobility, the host used was a blend of poly(N-vinyl carbazole) and 1,3-bis(2-(4-tert-butylphenyl)-1,3,4-oxadiazo-5-yl)benzene. Effect of using electron transport layer (ETL) with similar energy levels and different mobilities was also studied. The emissive layer has been characterized by UV–visible absorption spectroscopy, steady-state and time-resolved photoluminescence, field emission scanning electron microscopy, atomic force microscopy, and thickness profilometer. Films with TXO-TPA with the host were smoother as a result of good intermixing. The photoluminescence decay lifetimes of the blend with TXO-TPA are also longer as compared to that of Ir(ppy)3. Devices were also fabricated and the results were compared with the thin film emitter layer properties. Our results show that in spite of inferior morphology and emissive properties, the phosphorescent emitter Ir(ppy)3 devices show a superior luminance and lower turn-on voltage as compared to the devices with TADF emitter TXO-TPA. We attribute these to better LUMO level matching with the ETL and lower thickness. Photoluminescence spectra of different quantities of Ir(ppy)3 and TXO-TPA in host [ABSTRACT FROM AUTHOR]

There have been many advances in the development of thermally activated delayed fluorescence (TADF) materials for organic light emitting diode (OLED) applications in recent years. In particular, intramolecular exciplex systems have been highly studied and found to produce OLED devices of high external quantum efficiency (EQE) due to triplet harvesting via TADF. The proposed next generation of OLEDs uses hyperfluorescence to overcome the problem of broad emission associated with exciplexes. This process involves Förster resonance energy transfer (FRET) from the TADF host to a fluorescent dopant. In this work we revisited the photophysics of the TAPC:PBD exciplex (formed between the electron donor di-[4-(N , N -di- p -tolyl-amino)-phenyl]cyclohexane (TAPC) and the electron acceptor, 2-(4-biphenyl)-5-(4- tert -butylphenyl)-1,3,4-oxadiazole (PBD)) as a host capable of simultaneously performing triplet harvesting and work as a donor transferring energy to a bright fluorescent emitter. The aim is to investigate the interplay between energy transfer and intersystem crossing in this hyperfluorescence system. Contrarily to previous findings, films of the TAPC : PBD blend show relatively slow reverse intersystem crossing rate (RISC) and weak luminescence efficiency (PLQY). Despite this, when doped with the strong fluorescent emitter TTPA , the luminescence quantum yield is greatly improved due to the highly efficient energy transfer rate from TAPC : PBD to TTPA. The rapid FRET from the exciplex to the fluorescent emitter overcomes the non-radiative losses affecting the luminescence efficiency of the blend. This study shows that the hyperfluorescence mechanism not only allows colour purity in OLEDs to be optimised, but also facilitates suppressing major loss mechanisms affecting luminescence efficiency, thus creating conditions to maximizing EQE. [Display omitted] • A detailed photophysical study of the TAPC:PBD exciplex. • Exploration of the FRET mechanism to a fluorescent dopant TTPA. • Huge improvement of PLQY, from a poor triplet harvesting exciplex to a very bright hyperfluorescence system. [ABSTRACT FROM AUTHOR]

[Display omitted] Although OLEDs are widely employed nowadays for display technology devices, their application for room-lighting illumination remains a challenge due to the cost-effectiveness issues, mainly related to device fabrication. In this sense, the present study investigates the optimization of blue-emitting TADF (DMOC-DPS) and yellow-emitting TADF (TXO-TPA) compounds in solution-processed OLEDs to achieve efficient white light emission in a two-organic layer device. Four different host materials were studied, aiming to balance the charge mobility of holes and electrons. The host materials used include (in %wt.) a 1:1 mixture of mCP and DPEPO (HOST1), a 3:2 mixture of PVK and DPEPO (HOST2), a 3:2 mixture of PVK and mCP (HOST3), and a 3:2 mixture of PVK and butyl-PBD (HOST4). The experimental results obtained from the solution-processed OLEDs indicate that DMOC-DPS is predominantly a hole transport material, and hosts with predominantly n-type character, such as HOST1 and HOST4 , resulting in the most efficient white-OLEDs by the most balanced charge mobility. With structure optimization, WOLEDs achieved 6.43 % EQE with a brightness of 2621 cd/m2 (not integrated) and 6.06 % EQE with a brightness of 1986 cd/m2 for HOST4 and HOST1 , respectively. The emission characteristics were influenced by host materials characteristics, with blue and yellow emissions being fine-tuned to produce complementary colors. This study highlights the critical role of charge mobility balance in the emissive layer and demonstrates the potential of independently optimizing blue and yellow TADF components for high-performance WOLEDs suitable for indoor lighting applications. [Display omitted] • New approaches for solution-deposited WOLEDs based on complimentary color TADF emitters. • Electrical transport/recombination optimization in TADF host: guest WOLED deposited by solution-process techniques. • OLEDs simulation towards simplifyed/efficent device structure development. [ABSTRACT FROM AUTHOR]

Carbene-metal-amide (CMA) complexes based on cyclic(amino)(barrelene)carbene (CABC) ligands have been prepared for both Cu(I) and Au(I) metal centres. Synthetic protocols based on the conventional and microwave heating enabled ten-fold shorter reaction times and high yields of the CMA materials. Stabilization of the lowest unoccupied molecular orbital (LUMO) effects the electronic and photophysical properties. These materials benefit from short excited state lifetimes down to 0.9 μs and photoluminescence quantum yields up to 66 %. Nonradiative processes are revealed and associated with the rotational freedom of the aryl moiety in the CABC carbene ligand. Steady-state and time-resolved photoluminescence spectroscopy was used to estimate an activation energy barrier of 83 meV between singlet and triplet charge transfer (CT) excited states. Varied temperature photoluminescence confirms that 3CT photoluminescence remains even at 18 K, with no contribution from locally excited triplet states 3LE. Molecular design rules have been enhanced to propose bright thermally activated delayed fluorescence (TADF) CMA emitters. [Display omitted] • Microwave-assisted synthesis of carbene-metal-amide (CMA) materials in high yields. • Structure-property correlation to decipher the non-radiative process in CMA TADF materials. • Carbenes with high electrophilicity for future design of the red CMA TADF emitters. [ABSTRACT FROM AUTHOR]

Despite its simplicity, Boltzmann thermometry suffers from limited relative sensitivities since the energy gap must be in the order of magnitude of the thermal energy used for probing. Luminescent crossover thermometry is a potential alternative to exploit high energy gaps at low temperatures based on a generally high non-radiative coupling rate via a configurational crossover. The number of possible candidates for this type of temperature-dependent luminescence is quite versatile. Inorganic systems include transition metal ions with split d orbitals in a ligand field such as Cr3+ and Mn4+, mercury-like s2 ions such as Bi3+ or Pb2+ with coupled 3P0 and 3P1 levels, or lanthanoid ions with low energetic 4fn-15d1 levels next to their 4fn spin-orbit levels. In the case of organic emitters, thermally activated delayed fluorescence (TADF) has become increasingly popular, which relies on thermal coupling between an excited singlet and triplet state via intersystem crossing. While the general concept of two thermally excited radiatively emitting states is valid for each of the mentioned types of luminophores and thus, thermometry is in principle possible, the mechanistic details of the thermal coupling can be different. In this tutorial and theoretically motivated article, I will shortly review the relevant aspects of the excited state kinetics of two thermally coupled levels and demonstrate how the ratio between radiative and intrinsic non-radiative coupling rates affects the possible readout choices for optical signals used as a measure for temperature and how this influences the relative sensitivity of ratiometric and lifetime-based thermometers. An overview over various possible inorganic and organic emitters with the potential for thermometry will be given and based on these kinetic considerations, it will be assessed what readout mode is most recommendable for a given luminescent center.

Compared with the large number of single-function materials such as aggregation-induced emission (AIE), mechanochromic luminescence (MCL), or thermally activated delayed fluorescence (TADF) emitters, multifunctional emitting materials offer more opportunities in practical applications. In this report, we provide a simple molecular design strategy towards the conversion of a MCL building block to a multifunctional emitter. Through altering the substituent sites and increasing the number of electron donors and steric hindrance on a normal MCL backbone benzo[d,e]benzo[4,5]imidazo[2,1-a]isoquinolin-7-one, a novel multifunctional material 10,11-bis-(4-diphenylamino-phenyl)-benzo[d,e]benzo[4,5]imidazo[2,1-a]isoquinolin-7-one (10,11-2TPA-BBI) is designed and synthesized. 10,11-2TPA-BBI exhibits simultaneous polymorphism, AIE, MCL and TADF properties. It can form four different aggregate species: yellow solid (YS) and orange solid (OS), orange flake-shaped crystal (OC), and red prism-like crystal (RC). Among them, because of the small energy gaps (ΔESTs < 0.3 eV) between the singlet and triplet excited states, OS, OC and RC exhibit TADF properties, while YS show normal fluorescence characteristics with a large ΔEST of 0.33 eV. OS can be reversibly transformed into YS upon external stimuli, which can be attributed to the emission switch between local excited state and charge transfer state. Crystallographic study indicates that the bulky structure and weak intermolecular interactions account for polymorphism and AIE properties. This work will provide a simple molecular design strategy for multifunctional materials.

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 (T2) 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 (T1).

[Display omitted] • Isomeric pairs of 2,3- and 3,4-triptycene (Tp) fused multi-resonance TADF emitters were prepared. • The 3,4-Tp-fused emitter exhibits 6-fold faster reverse intersystem crossing (RISC) but shows PL spectral broadening compared to the 2,3-isomer. • Stronger SOC between the S 1 and T 2 excited states, as well as smaller activation energy of RISC, is observed for the 3,4-Tp-fused emitter. • Blue TADF-OLEDs based on each isomeric emitter similarly achieve a high maximum EQE of ∼ 26 %. • The devices with the 3,4-isomer exhibit significantly reduced efficiency roll-offs compared to the 2,3-isomer. Concurrently achieving high efficiency, narrowband emission, and low efficiency roll-off remains a challenging task for realizing stable blue organic light-emitting diodes (OLEDs) with high color purity. To tackle this issue, herein, two isomeric pairs of B,N-doped multi-resonance thermally activated delayed fluorescence (MR-TADF) emitters, namely, 2,3-Tp-BuDABNA-R and 3,4-Tp-BuDABNA-R (R=H, 3,5-Xyl), featuring triptycene (Tp) moieties fused into the 2,3- and 3,4-positions of the B,N core, respectively, are presented. Both isomeric forms exhibit blue emissions with near-unity photoluminescence (PL) quantum yields in their doped host films. Notably, the 3,4-Tp-fused emitter shows 6-fold faster reverse intersystem crossing (RISC) compared to the 2,3-Tp-fused emitter, albeit with PL spectral broadening. Along with a smaller activation energy of RISC, the stronger spin–orbit coupling between the singlet (S 1) and triplet (T 2) excited states of the 3,4-Tp-fused emitter is suggested to facilitate the RISC process. Furthermore, a high-frequency vibration in the Tp-fused benzene ring, accompanied by a large reorganization energy, is found to mainly contribute to the spectral broadening of the 3,4-Tp-fused emitter. Blue TADF-OLEDs based on each isomeric emitter similarly achieve a high maximum external quantum efficiency of ∼ 26%. Remarkably, the devices with the 3,4-isomer exhibit significantly reduced efficiency roll-offs compared to the 2,3-isomer, demonstrating that isomer engineering of MR emitters can have a distinct impact on controlling device performance. [ABSTRACT FROM AUTHOR]

Exploring through-space charge transfer (TSCT) excited state for the design of thermally activated delayed fluorescence (TADF) emitters has been receiving increasing interest for organic light-emitting diodes (OLEDs). In this work, we developed two TSCT-TADF molecules, namely 2DPXZ-QX and 2DPXZ-DFQX , which have sandwich-type donor-acceptor-donor (D-A-D) structures supported by two carbazole bridges. Dibenzo[a,c]phenazine (QX) and its fluorinated derivative (DFQX) were used as the acceptors and O-bridged triphenylamine (DPXZ) was used as the donor. The two donors and acceptor in each molecule are aligned in a face-to-face orientation and thus result in the presence of intramolecular π–π interactions, as revealed by their single crystal X-ray structures. The emission maxima (λ PL) of 2DPXZ-QX and 2DPXZ-DFQX in doped 1,3-bis(N-carbazolyl)benzene films are 595 and 600 nm with photoluminescence quantum yields of 67 % and 54 %, respectively. The delayed fluorescence lifetimes are 8.8 and 6.7 μs. OLEDs based on the new sandwich-type emitters show maximum external quantum efficiencies of up to 19.1 %. [Display omitted] • Cofacial donor-acceptor-donor for through-space charge transfer excited states. • Balanced radiative decay and reverse intersystem crossing rate constants. • Improved thermally activated delayed fluorescence owing to strong π-π interactions. • Red organic light-emitting diodes with high external quantum efficiencies. [ABSTRACT FROM AUTHOR]

Long persistent luminescence (LPL) including thermally activated delayed fluorescence (TADF) and phosphorescence is widely applied in luminogens. Recently, Pan et al. pioneered the discovery of TADF and phosphorescence in the HPI2C molecule by manipulating temperature in line with the excited-state intramolecular proton transfer (ESIPT) dynamics (J. Am. Chem. Soc. 2022, 144, 2726). They blazed a new trail to explore the switching mechanism between TADF and phosphorescence in single molecule. Nevertheless, luminescence mechanism for HPI2C cannot be explained solely through experimental means. Theoretically, we demonstrate that the ESIPT and photocyclization channel induced conical intersection processes facilitate the fluorescence quenching of the Enol* state. Moreover, we prove the cruciality of the T 2 state in the TADF phenomenon involved in Keto* state and reconsider the mechanism of the dual phosphorescence. Our investigation is favorable to provide theoretical support for the design of the LPL materials based on the ESIPT-attributed molecules. [Display omitted] • The ESIPT process and peaked conical intersection facilitate the fluorescence quenching of the Enol* state. • The T 2 state plays a predominant role in TADF phenomenon involved in Keto* state. • The anti-Kasha mechanism of dual phosphorescence is reconsidered. [ABSTRACT FROM AUTHOR]

This work describes the synthesis and characterisation of new tetrahedral boron complexes, incorporating bromine- or iodine-substituted 8-quinolinolato chelate chromophores connected to 9-borafluoren-9-yl or diphenylboron orthogonal fragments. The molecular features and photophysical properties of these complexes are analysed in both solution and solid state. Steady-state photophysical studies reveal photoluminescence quantum yields (Φ f) ranging from 0.02 to 0.15 and prompt fluorescence (PF) lifetimes (τ f) between 2 and 16 ns. Time-resolved photophysical experiments show the presence of delayed fluorescence (DF) and phosphorescence at both 77 K and room temperature. The DF intensity increases with a rise in temperature. This variation is ascribed to an enhancement in the intersystem crossing (ISC) process promoted by the bromine or iodine heavy-atom effect. Investigations into the dependence of DF intensity relative to the excitation dose indicate emissions stemming either from Triplet-Triplet Annihilation (TTA), Thermally Activated Delayed Fluorescence (TADF), or a combination of these competing mechanisms. The effect is related to the size and number of heavy-atom substituents in each boron complex. A study of the DF emission intensity as a function of the excitation dose reveals that diiodo-substituted 8-quinolinolato boron complexes, whether rigid or flexible, display TADF emission. Rigid 5,7-dibromo- and 5-chloro-7-iodo-substituted 8-quinolinolato complexes exhibit a combined TADF-TTA mechanism, whereas the other complexes predominantly demonstrate pure TTA emission. DFT and TDDFT calculations showed that the ground state structures reproduced the experimental geometries and only small increases in bond lengths were observed in the excited state geometries. The low energy absorption bands displayed mainly intra-ligand π→π* (8-quinolinato) character. The fluorescence emission energies were well reproduced, while the singlet-triplet energy gaps were relatively high and spin-orbit coupling was relevant for complexes with heavy-atoms. Ultimately, organic light-emitting diodes (OLEDs) are fabricated using the most luminescent boron complexes. The best OLED is obtained when using complex 3a , which displays green electroluminescence (EL) (λ EL = 502 nm) with maximum external quantum efficiency (EQE max) of 2.5% and maximum luminance (L max) of 2200 cd m−2. • New boron complexes with Br- or I-substituted 8-quinolinolato ligands were prepared. • DFT/TDDFT calculations revealed 8-quinolinolato intra-ligand electronic transitions. • The new boron complexes exhibited Delayed Fluorescence (DF). • The DF arises from either TTA, TADF or mixed TTA-TADF processes. • Selected boron complexes were tested as dopants in OLED devices. [ABSTRACT FROM AUTHOR]

There are many reports on thermally activated delayed fluorescence (TADF) organic light-emitting diodes (OLEDs) with the external quantum efficiency achieving 30%. We investigate the electrical conduction of 4CzIPN-based TADF OLEDs depending on doping concentration of 0, 10, 20 or 35 mol%. As the doping concentration of 4CzIPN is increased, the electrons injected into the 4CzIPN sites are easily hopping between the 4CzIPN sites. The drive voltage decreases but the power efficiency is not remarkably improved. Since the red-shift of EL spectra at a constant current density is observed with doping concentration, the main carrier recombination zone is found to move with doping concentration. [ABSTRACT FROM AUTHOR]

The employment of thermally activated delayed fluorescence (TADF) emitters is one of the most promising ways to realize the external quantum efficiency (EQE) of over 25% for organic light-emitting diodes (OLEDs). In addition, the TADF emitter based on oxygen-bridged boron (BO) fragment can maintain blue emission with high color purity. Herein, we constructed two blue TADF emitters, 3TBO and 5TBO, for OLEDs application. Both emitters consist of three donors linked at the oxygen-bridged boron acceptor. OLED devices based on 3TBO and 5TBO exhibited both high excellent device efficiency and high color purity with a maximum EQE; full-width at half-maximum (FWHM); and CIE coordinates of 17.3%, 47 nm, (0.120, 0.294), and 26.2%, 57 nm, (0.125, 0.275), respectively. [ABSTRACT FROM AUTHOR]

Due to the strong concentration quenching effect, the development of non-doped devices with excellent performance is limited. Herein, a novel thermally activated delayed fluorescence (TADF) emitter which contain Spiro[anthracene-9(10H),9’-[9H]fluoren]-10-one (9-FAO) and 9,9-dimethyl-9,10-dihydroacridine (DMAC) was designed and synthesized. The compound shows TADF characteristics which can be observed by transient PL decay tests. By introducing DMAC into the para-position of the 9-FAO which has a highly twisted structure, the distance between the molecules increases to inhibit concentration quenching. The non-doped OLED device by using 2-(9, 9-dimethylacridin-10(9H)-yl)-10H-spiro[anthracene-9,9’- fluoren]-10-one (DMTO-DMAC) as emitter achieved a superior current efficiency of 35.6 cd Aâˆ'1 and maximum external quantum efficiency of 11.3% with an emission peak at 516 nm. This work demonstrates the feasibility of increasing intermolecular distance to obtain highly efficient non-doped devices. [ABSTRACT FROM AUTHOR]

Hyperfluorescence™ (HF), known as the most advanced OLED emitting technology, combines TADF and fluorescence mechanisms enabling 100% internal quantum efficiency (IQE) and narrowband emission. Based on in silico simulation, HF is not only more outperformed than the modern OLED emitting technologies but also feasible for the RGB definition of BT.2020. Of the green top‐emission HF device, the device performance is manifold increased than that of the bottom‐emission, where this effect is more amplified than that in phosphorescence system. An efficiency improvement approach to reach market requirements was illustrated to show our vision in pursuing excellent performance. [ABSTRACT FROM AUTHOR]

An electroplex is an excited state charge transfer complex formed between a donor molecule and an acceptor molecule upon electrical excitation. Since the spatial overlap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of electroplex is small likewise exciplex, the energy difference between the singlet and the triplet charge transfer (1CT and 3CT) states can be very small, which facilitate the conversion of triplet excitons into singlet excitons by the assistance of thermal energy and the emission as delayed fluorescence. However, in contrast to exciplex, the detailed analysis of the reverse intersystem crossing (RISC) from 3CT to 1CT and the exciton‐related annihilation processes in electroplex OLEDs have been rarely reported. In this talk, the magnetic field effects (MFEs) on the electroplex host using 2,2'‐di(9H‐carbazol‐9‐yl)‐1,1'‐biphenyl (oCBP) and 9‐(4,6‐bis(3‐(triphenylsilyl)phenyl)‐1,3,5‐triazin‐2‐yl)‐9H‐carbazole (DSiCzTrz) were investigated. Temperature‐dependent MFE measurements revealed that RISC channel co‐exists with the intersystem crossing (ISC) channel and triplet‐polaron quenching process prevails in the electroplex EML. It was also found that 3CT excitons behave as charge scattering sites. [ABSTRACT FROM AUTHOR]

We report three deep blue multiple resonant TADF emitters, m‐ν‐DABNA, 4F‐ν‐DABNA, and 4F‐m‐ν‐DABNA by incorporating methyl groups and fluorine atoms in diboron based ν‐DABNA core. The introduction of methyl groups and fluorine atoms resulted in bandgap enhancement by electron donating and electron withdrawing effects. All three emitter's exhibit pure blue emissions with high photoluminescence quantum yield around ~90%, small ΔEST (≤ 0.07 eV) values, and fast reverse intersystem crossing rate (kRISC). Fabricated OLEDs with these emitters show excellent external quantum efficiency over 33%. Among three materials, 4F‐ν‐DABNA and 4F‐m‐ν‐DABNA exhibit the CIE y coordinate of 0.08 and 0.06, respectively. [ABSTRACT FROM AUTHOR]

Green and red hyperfluorescent devices meeting the B.T. 2020 standard have been achieved by appropriate device engineering. Further, a high performance full‐fluorescent R/G/B solution with a 96.5% coverage of B. T. 2020 color gamut is developed in this work, which is estimated to basically satisfy requirement of mass production. [ABSTRACT FROM AUTHOR]

The mechanism of thermally activated delayed fluorescence (TADF) in dendrimers is not clear. We report that fully‐conjugated or fully‐nonconjugated structures cause unwanted degenerate excited states due to multiple identical dendrons, which limit their TADF efficiency. We have synthesized asymmetrical "half‐dendronized" and "half‐dendronized‐half‐encapsulated" emitters. By eliminating degenerate excited states, the triplet locally excited state is ≥0.3 eV above the lowest triplet charge‐transfer state, assuring a solely thermal equilibrium route for an effective spin‐flip process. The isolated encapsulating tricarbazole unit can protect the TADF unit, reducing nonradiative decay and enhancing TADF performance. Non‐doped solution‐processed devices reach a high external quantum efficiency (EQEmax) of 24.0 % (65.9 cd A−1, 59.2 lm W−1) with CIE coordinates of (0.24, 0.45) with a low efficiency roll‐off and EQEs of 23.6 % and 21.3 % at 100 and 500 cd m−2. [ABSTRACT FROM AUTHOR]

The trifluoromethyl group has been previously explored as a non-conjugated electron-withdrawing group in donor–acceptor thermally activated delayed fluorescence (TADF) emitters. In the present study, we investigate computationally the potential of other fluorine-containing acceptors, trifluoromethoxy (OCF3), trifluoromethylthio (SCF3), and pentafluorosulfanyl (SF5), within two families of donor–acceptor TADF emitters. Time-dependent density functional theory calculations indicate that when only two ortho-disposed carbazole donors are used (Type I molecules), the lowest-lying triplet state possesses locally excited (LE) character while the lowest-lying singlet state possesses charge-transfer character. When five carbazole donors are present in the emitter design (Type II molecules), now both S1 and T1 states possess CT character. For molecules 2CzOCF3 and 5CzOCF3, the singlet energies are predicted to be 3.92 eV and 3.45 eV; however, the singlet-triplet energy gaps, ΔESTs, are predicted to be large at 0.46 eV and 0.37 eV, respectively. The compounds 2CzCF3, 2CzSCF3, and 2CzSF5, from Type I molecules, show significant promise as deep blue TADF emitters, possessing high calculated singlet energies in the gas phase (3.62 eV, 3.66 eV, and 3.51 eV, respectively) and small, ΔESTs, of 0.17 eV, 0.22 eV, and 0.07 eV, respectively. For compounds 5CzSCF3 and 5CzSF5, from Type II molecules, the singlet energies are stabilized to 3.24 eV and 3.00 eV, respectively, while ΔESTs are 0.27 eV and 0.12 eV, respectively, thus both show promise as blue or sky-blue TADF emitters. All these six molecules possess a dense number of intermediate excited states between S1 and T1, thus likely leading to a very efficient reverse intersystem crossing in these compounds.

Due to the energy gap law, the direct fabrication of efficient organic afterglow materials with long emission wavelengths at ambient conditions remains challenging. Here, luminescent dopants with moderate kRISC values of 100–101 s−1 are designed to harvest triplet energies, simultaneously improving afterglow efficiency and maintaining emission lifetimes >0.1 s. Organic matrices with large dipole moments are selected to populate the triplet excited states of the luminescent dopants and suppress their nonradiative decay and quenching. The dopant‐matrix systems exhibit TADF‐type organic afterglow with quantum efficiency of 20% to 60% and emission wavelengths exceeding 600 nm. Because of their singlet excited state nature, the TADF‐type afterglow emitters can efficiently transfer excited energy to rhodamine B or cyanine 5.5 fluorescence dyes for the construction of red and near‐infrared afterglow materials which display promising bioimaging applications. [ABSTRACT FROM AUTHOR]

In this study, HATCN is coated on flexible PET/indium tin oxide (ITO) substrate as a modified layer and a hole injection layer to improve the hole injection from ITO. Then a blue organic light emitting diode (OLED) can successfully be fabricated without a surface treatment procedure (O2 plasma or UV Ozone treatment). The new blue TADF series fluorescent material is employed as emitting layer with a luminescence wavelength of 456 nm. Also, it has a narrow full width at a half maximum (FWHM) of 26 nm featuring excellent color chromaticity. Quantum dot (QD) photoresist is a perfect color conversion material featuring good color adjustability, narrow emission spectrum, high luminous efficiency, and simple spin-coating processes. In this study, the photoresist mixed with green and red quantum dots is used as a color conversion layer (CCL), and a blue OLED is utilized to excite green and red CCL. To test the material of QD photoresist, it is coated on the substrate of another piece of glass first and then the blue OLED is utilized to remotely excite green and red QD CCL. The fluorescence characteristic of QD photoresist is explored to acquire a spectrum of 528 nm and 620 nm. In the device structure of a blue OLED, the electron-and hole-only current density is compared and the hole transport layer TAPC thickness is adjusted to improve the luminance and efficiency. Finally, green and red quantum dot photoresist is mixed using a proper ratio and then directly coated on the back of the PET/ITO substrate. Furthermore, the thickness of the QD photoresist is adjusted to increase the QD excited fluorescence. The blue OLED and QD CCL was integrated to generate three primary colors, i.e., blue, green, and red. Finally, a flexible white OLED lighting panel is successfully fabricated using simple processes. Moreover, it features high-spectrum stability. The CIE coordinates will not drift with bias, thus, it can resist the voltage variation. [ABSTRACT FROM AUTHOR]

Understanding of relationship between structure and property of thermally activated delayed fluorescence (TADF) materials is essential for developing efficient TADF materials. To investigate the substituent effect of electron donors on luminescent properties of TADF materials, a series of single crystals based on triphenylamine (TPA)/anthraquinone (AQ) hybrids namely 1-TPA-AQ, 2-TPA-AQ, 1,8-2TPA-AQ, 2,6-2TPA-AQ have been prepared in this work. Interestingly, it is demonstrated that the substituent site of TPA unit has an important impact on the conformation of AQ for the first time. The planarity of the AQ units in these four molecules is in the order 2,6-2TPA-AQ > 2-TPA-AQ ≈ 1-TPA-AQ > 1,8-2TPA-AQ, which is associated with the molecule symmetry. In addition, intermolecular interactions in these crystals are also investigated. In α-substituted AQ derivatives (1-TPA-AQ and 1,8-2TPA-AQ) typical π–π intermolecular interactions may account for their normal TADF but weak emission in solid state. In contrast, β-substituted AQ derivatives (2-TPA-AQ and 2,6-2TPA-AQ) display weak intermolecular interactions, which are beneficial to restricting molecular motions and to suppressing the non-radiative decay, resulting in efficient TADF and aggregation-induced emission properties simultaneously. It is demonstrated that the substituent site of triphenylamine unit on anthraquinone (AQ) group has an important impact on the conformation of AQ. [ABSTRACT FROM AUTHOR]

Four new zinc(II) Schiff base complexes with carbazole electron donor units and either a 2,3-pyrazinedicarbonitrile or a phthalonitrile acceptor unit were synthesized. The donor units are equipped with two bulky 2-ethylhexyl alkyl chains to increase the solubility of the complexes in organic solvents. Furthermore, the effect of an additional phenyl linker between donor and acceptor unit on the photophysical properties was investigated. Apart from prompt fluorescence, the Schiff base complexes show thermally activated delayed fluorescence (TADF) with quantum yields up to 47%. The dyes bearing a phthalonitrile acceptor emit in the green–yellow part of the electromagnetic spectrum and those with the stronger 2,3-pyrazinedicarbonitrile acceptor—in the orange–red part of the spectrum. The emission quantum yields decrease upon substitution of phthalonitrile with 2,3-pyrazinedicarbonitrile and upon introduction of the phenyl spacer. The TADF decay times vary between 130 µs and 3.5 ms at ambient temperature. The weaker phthalonitrile acceptor and the additional phenyl linker favor longer TADF decay times. All the complexes show highly temperature-dependent TADF decay time (temperature coefficients above −3%/K at ambient conditions) which makes them potentially suitable for application as molecular thermometers. Immobilized into cell-penetrating RL-100 nanoparticles, the best representative shows temperature coefficients of −5.4%/K at 25 °C that makes the material interesting for further application in intracellular imaging. [ABSTRACT FROM AUTHOR]

Pure organic molecules based thermally activated delayed fluorescence (TADF) emitters have been successfully developed in recent years for their propitious application in highly efficient organic light emitting diodes (OLEDs). In the case of orange red emitters, the non‐radiative process is known to be a serious issue due to its lower lying singlet energy level. However, recent studies indicate that there are tremendous efforts put to develop efficient orange red TADF emitters. In addition, the external quantum efficiency (EQE) of heteroaromatic based orange red TADF OLEDs surpassed 30 %. Such heteroaromatic type emitters showed wide emission spectra; therefore, more attention is being paid to develop highly efficient orange red TADF emitters along with good color purity. Herein, the recent progress of orange red TADF emitters based on molecular structures, such as cyanobenzene, heteroaromatic, naphthalimide, and boron‐based acceptors, are reviewed. Further, our insight on these acceptors has been provided by their photophysical studies and device performances. Future perspectives of orange red TADF emitters for real practical applications are discussed. [ABSTRACT FROM AUTHOR]

In this study, two new donor-acceptor type thermally activated delayed fluorescence materials using carbazole as a donor and cyano substituted benzene as an acceptor were synthesized. Structural parameters, molecular orbital densities, photophysical characteristics were determined. By changing the substitution position of the cyano groups on the phenyl rings, the relationship between structure and properties was also be disclosed. These materials were tested as emissive species for the fabrication of organic light-emitting diodes. The blue devices showed EL emission peaks at 464 and 488 nm with the CIE coordinates of (0.17, 0.18) and (0.21, 0.31), respectively. [ABSTRACT FROM AUTHOR]

Solution-processed devices with thermally activated delayed fluorescence (TADF) compounds have gained great attention due to their low cost and high performance. Here, two solution-processable TADF emitters named ACCz-DPyM and POxCz-DPyM were synthesized by coupled 9,10-dihydro-9,9-dimethylacridine or phenoxazine modified carbazole as donor with di(pyridin-3-yl)methanone as acceptor. Both TADF compounds show same small ΔΕST of 0.04 eV and high PLQY of 66.2% and 58.2%. The devices fabricated by ACCz-DPyM and POxCz-DPyM as emitters show excellent performance as solution-processed with low turn-on voltage of 4.0 and 3.4 V, high luminance of 6209 and 3248 cd m−2 at 8 V, the maximum current efficiency of 9.9 and 15.9 cd A−1, the maximum external quantum efficiency of 6.6% and 6.5% and low efficiency roll-off. The solution-processed device based on ACCz-DPyM shows bluish-green emission. These results show that ACCz-DPyM and POxCz-DPyM are suitable for solution processing devices.

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 (T 1 ) to the singlet state (S 1 ). Therefore, TADF emitters enabling activated and long lifetime T 1 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., (© 2024 Wiley‐VCH GmbH.)

Tetrahydro-4 H -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.