Aromatic-Imide-Based Thermally Activated Delayed Fluorescence Materials for Highly Efficient Organic Light-Emitting Diodes

Dual Emission and Low-Temperature Afterglow in Xanthone-Dibenzoazepine for High EQE Host-Guest OLEDs with Low-Efficiency Roll-Off

Research has been driven to demonstrate organic light-emitting diodes (OLEDs) with high efficiency, and in the quest for new materials, thermally activated delayed fluorescence (TADF) emitters have been employed. Preparation of donor-acceptor (D-A) π-conjugates is a useful guideline for developing TADF emitters. TADF emitters have shown excellent progress and high maximum external quantum efficiency (EQEmax) for OLEDs in the recent past; however, they suffer with substantial roll-off resulting in a decrease in their efficiency. In order to have efficient OLED emitters with less efficiency roll-off, we designed a xanthone-amine derivative with twisted electron-rich dibenzoazepine having limited rotation at the donor-acceptor bond. Xan-Azepine shows solvent polarity-dependent fluorescence in the range of 441- 597 nm having a lifetime below 10 ns. At 77 K in Me-THF, a triplet at 557 nm was observed having a decay lifetime of 0.75 s and an afterglow for about 6 s. In powder, it shows dual emission, i.e., fluorescence (490 and 6 ns) and phosphorescence (530 nm and 192 μs) at ambient conditions. The energy difference between the singlet and triplet energy levels of Xan-Azepine is found to be 0.18 eV in the powder sample. Its blend in 4,4'-bis(N-carbazolyl)-1,1'-biphenyl (CBP) showed delayed fluorescence with a lifetime of 118 μs at 300 K, while it reduced to 84 μs at 150 K. These observations suggest the TADF nature of Xan-Azepine in its CBP blend. OLED devices of Xan-Azepine showing a turn-on voltage of 2.8 V and a EQEmax of 12% were successfully fabricated. In the doped films of Xan-Azepine (5 wt %) with CBP, a maximum luminescence of 5980 Cd/m2 at a current density of 70 mA/cm2 was obtained, resulting in devices with low-efficiency roll-off (2.75%).

Donor engineering to regulate fluorescence of a symmetrical structure based on a fluorene bridge for white light emission

A white organic light-emitting device (WOLED) obtained using blue and yellow complementary colors possesses extremely high optical efficiency. We designed and prepared a completely symmetric D-π-D type efficient blue light small molecule FFA based on octylfluorene as a π bridge, where the undoped device showed efficient blue organic light-emitting device (OLED) performance with a maximum emission wavelength of 428 nm, Commission Internationale de l'Eclairage (CIE) coordinates of (0.17, 0.11) and one of the narrowest full width at half maximum (FWHM) of 35 nm. To improve the matching measure of complementary color materials for achieving white light emission, a yellow light small molecule FCzA was prepared by adjusting the conjugation degree of peripheral electron-donating groups based on the same fluorene-based π bridge with FFA. Undoped devices based on FCzA demonstrated an electroluminescence (EL) emission peak at 576 nm with CIE coordinates of (0.43, 0.49) and a relatively wide FWHM of 130 nm. Ultimately, the white OLED device was modulated with CIE coordinates located at (0.33, 0.38) via proportional regulation with a mixture of FFA and FCzA in a ratio of 10 : 3 as the light-emitting layer.

Multiple-resonance thermally activated delayed fluorescence materials based on phosphorus central chirality for efficient circularly polarized electroluminescence

Circularly polarized organic light-emitting diodes (CP-OLEDs) hold great potential for naked-eye 3D displays, necessitating efficient chiral luminescent materials with an optimal CP luminescence (CPL) dissymmetry factor (g). Herein, we present the first chiral multiple resonance thermally activated delayed fluorescence (MR-TADF) materials containing a phosphorus chiral center by incorporating 5-phenylbenzo[b]phosphindole-5-oxide into the para-position of two MR-TADF cores. The compounds, NBOPO and NBNPO, exhibit photoluminescence peaks at 462 and 498 nm with narrow full-width at half-maximum values of 25 and 24 nm in toluene, respectively. Notably, (R/S)-NBOPO and (R/S)-NBNPO enantiomers display high quantum yields of 87% and 93% and symmetric CPL with |gPL| factors of 1.18 × 10-3 and 4.30 × 10-3, respectively, in doped films. Moreover, the corresponding CP-OLEDs show impressive external quantum efficiencies of 16.4% and 28.3%, along with symmetric CP electroluminescence spectra with |gEL| values of 7.0 × 10-4 and 1.4 × 10-3, respectively.

Phosphorescent PdII-PdII Emitter-Based Red OLEDs with an EQEmax of 20.52

Three dinuclear Pd(II) complexes (1, 2, and 3) with intense red phosphorescence at room temperature are here synthesized using strong ligand field strength compounds. All three complexes are characterized by nuclear magnetic resonance, high-resolution mass spectrometry, and elemental analyses. Complexes 2 and 3 are characterized by single-crystal X-ray diffraction. The crystalline data of 2 and 3 reveal complex double-layer structures, with Pd-Pd distances of 2.8690(9) Å and 2.8584(17) Å, respectively. Furthermore, complexes 1, 2, and 3 show phosphorescence at room temperature in their solid states at the wavelengths of 678, 601, and 672 nm, respectively. In addition, they show phosphorescence at 634, 635, and 582 nm, respectively, in the 2 wt.% (PMMA) films, and phosphorescence at 670, 675, and 589 nm, respectively, in the deoxygenated CH2Cl2 solutions. Among three complexes, complex 1 shows red emission at 634 nm with phosphorescent quantum yield Ф = 67% in the 2 wt.% PMMA film. Furthermore, complex 1-based organic light-emitting diode is fabricated using a vapor-phase deposition process, and their maximum external quantum efficiency reaches 20.52%, which is the highest percentage obtained by using the dinuclear Pd(II) complex triplet emitters with the CIE coordinates of (0.62, 0.38).

An unprecedented roll-off ratio in high-performing red TADF OLED emitters featuring 2,3-indole-annulated naphthalene imide and auxiliary donors

The capability of organic emitters to harvest triplet excitons via a thermally activated delayed fluorescence (TADF) process has opened a new era in organic optoelectronics. Nevertheless, low brightness, and consequently an insufficient roll-off ratio, constitutes a bottleneck for their practical applications in the domain of organic light-emitting diodes (OLEDs). To address this formidable challenge, we developed a new design of desymmetrized naphthalimide (NMI) featuring an annulated indole with a set of auxiliary donors on its periphery. Their perpendicular arrangement led to minimized HOMO-LUMO overlap, resulting in a low energy gap (ΔE ST = 0.05-0.015 eV) and efficient TADF emission with a photoluminescence quantum yield (PLQY) ranging from 82.8% to 95.3%. Notably, the entire set of dyes (NMI-Ind-TBCBz, NMI-Ind-DMAc, NMI-Ind-PXZ, and NMI-Ind-PTZ) was utilized to fabricate TADF OLED devices, exhibiting yellow to red electroluminescence. Among them, red-emissive NMI-Ind-PTZ, containing phenothiazine as an electron-rich component, revealed predominant performance with a maximum external quantum efficiency (EQE) of 23.6%, accompanied by a persistent luminance of 38 000 cd m-2. This results in a unique roll-off ratio (EQE10 000 = 21.6%), delineating a straightforward path for their commercial use in lighting and display technologies.

B-N Covalent Bond Embedded Double Hetero-[n]helicenes for Pure Red Narrowband Circularly Polarized Electroluminescence with High Efficiency and Stability

Chiral B/N embedded multi-resonance (MR) emitters open a new paradigm of circularly polarized (CP) organic light-emitting diodes (OLEDs) owing to their unique narrowband spectra. However, pure-red CP-MR emitters and devices remain exclusive in literature. Herein, by introducing a B-N covalent bond to lower the electron-withdrawing ability of the para-positioned B-π-B motif, the first pair of pure-red double hetero-[n]helicenes (n = 6 and 7) CP-MR emitter peaking 617 nm with a small full-width at half-maximum of 38 nm and a high photoluminescence quantum yield of ≈100% in toluene is developed. The intense mirror-image CP light produced by the enantiomers is characterized by high photoluminescence dissymmetry factors (gPL ) of +1.40/-1.41 × 10-3 from their stable helicenes configuration. The corresponding devices using these enantiomers afford impressive CP electroluminescence dissymmetry factors (gEL ) of +1.91/-1.77 × 10-3 , maximum external quantum efficiencies of 36.6%/34.4% and Commission Internationale de I'Éclairage coordinates of (0.67, 0.33), exactly satisfying the red-color requirement specified by National Television Standards Committee (NTSC) standard. Notably a remarkable long LT95 (operational time to 95% of the initial luminance) of ≈400 h at an initial brightness of 10,000 cd m-2 is also observed for the same device, representing the most stable CP-OLED up to date.

Research and Design of Aggregation-Regulated Thermally Activated Delayed Fluorescence Materials for Time-Resolved Two-Photon Excited Fluorescence Imaging and Biological Monitoring

Exploring the nature of aggregation-regulated thermally activated delayed fluorescence (TADF) and proposing effective design strategies for two-photon excited TADF materials for time-resolved biological imaging and monitoring are urgent and encouraging. In this work, it is found that the aggregation effect not only plays an important role in decreasing the internal conversion decay rate but also strongly influences the singlet-triplet excited-state energy difference as well as the intersystem crossing rate. It is proposed that the transformation from prompt fluorescence materials to long lifetime TADF or phosphorescence materials can be accomplished by regulating the position of substituent groups, which provides an effective method to design and develop long afterglow materials. Then, a high-performance TADF compound with a large two-photon absorption cross section in the biological window (112 GM/775 nm), high TADF efficiency (nearly 100%), and long fluorescence lifetime (50.75 μs) has been designed, which demonstrates the potential application in time-resolved two-photon excited fluorescence imaging and biological detection.

V-shaped donor-acceptor organic emitters. A new approach towards efficient TADF OLED devices

We report the synthesis and characterization of a series of donor-acceptor TADF emitters with a new architecture, where the donor moiety and the dibenzazepine-based acceptor moiety are separated by a phenylene linker in a V-shaped spatial arrangement. Such spatial separation and electronic decoupling between the donor and the acceptor moieties leads to low singlet-triplet energy gaps and favors efficient exciton up-conversion.

Aggregation-Induced Emission Metallocuboctahedra for White Light Devices

Materials for organic light-emitting devices which exhibit superior emission properties in both the solution and solid states with a high fluorescence quantum yield have been extensively sought after. Herein, two metallocages, S1 and S2, were constructed, and both showed typical aggregation-induced emission (AIE) features with intense yellow fluorescence. By adding blue-emissive 9,10-dimethylanthracene, pure white light emission can be produced in the solution of S1 and S2. Furthermore, due to the remarkable AIE feature and good fluorescence quantum yield in the solid state, metallocages are highly emissive in the solid state and can be utilized to coat blue LED bulbs or integrate with blue-emitting chips to obtain white light. This study advances the usage of metallocages as practical solid-state fluorescent materials and provides a fresh perspective on highly emissive AIE materials.

Donor-Acceptor Type of Fused-Ring Thermally Activated Delayed Fluorescence Compounds Constructed through an Oxygen-Containing Six-Membered Ring

Nowadays, thermally activated delayed fluorescence (TADF) compounds with a fused-ring core skeleton are getting increasing research interest because of their use in high-performance organic light-emitting diodes (OLEDs). In this study, TADF compounds featuring a D-A-type fused-ring core skeleton are developed. The challenging compatibility of a planarized D-A arrangement and the TADF property is achieved through linking the D and A moieties with two oxygen atoms within a six-membered ring. Compared with a single-oxygen analogue possessing a flexible skeleton and a twisted D-A arrangement, these fused-ring compounds with higher skeleton rigidity show higher photoluminescence quantum yields and narrower emission spectra in toluene and in doped thin films. Their electroluminescent devices achieve high external quantum efficiencies (up to 19.4%), suggesting the potential of rarely achieved D-A-type fused-ring TADF systems to serve as high-performance emitters of OLEDs.

Naphthalimide-phenothiazine dyads: effect of conformational flexibility and matching of the energy of the charge-transfer state and the localized triplet excited state on the thermally activated delayed fluorescence

In order to investigate the joint influence of the conformation flexibility and the matching of the energies of the charge-transfer (CT) and the localized triplet excited (3LE) states on the thermally activated delayed fluorescence (TADF) in electron donor-acceptor molecules, a series of compact electron donor-acceptor dyads and a triad were prepared, with naphthalimide (NI) as electron acceptor and phenothiazine (PTZ) as electron donor. The NI and PTZ moieties are either directly connected at the 3-position of NI and the N-position of the PTZ moiety via a C-N single bond, or they are linked through a phenyl group. The tuning of the energy order of the CT and LE states is achieved by oxidation of the PTZ unit into the corresponding sulfoxide, whereas conformation restriction is imposed by introducing ortho-methyl substituents on the phenyl linker, so that the coupling magnitude between the CT and the 3LE states can be controlled. The singlet oxygen quantum yield (ΦΔ) of NI-PTZ is moderate in n-hexane (HEX, ΦΔ = 19%). TADF was observed for the dyads, the biexponential luminescence lifetime are 16.0 ns (99.9%)/14.4 μs (0.1%) for the dyad and 7.2 ns (99.6%)/2.0 μs (0.4%) for the triad. Triplet state was observed in the nanosecond transient absorption spectra with lifetimes in the 4-48 μs range. Computational investigations show that the orthogonal electron donor-acceptor molecular structure is beneficial for TADF. These calculations indicate small energetic difference between the 3LE and 3CT states, which are helpful for interpreting the ns-TA spectra and the origins of TADF in NI-PTZ, which is ultimately due to the small energetic difference between the 3LE and 3CT states. Conversely, NI-PTZ-O, which has a higher CT state and bears a much more stabilized 3LE state, does not show TADF.

Novel Polycyclic Fused Amide Derivatives: Properties and Applications for Sky-blue Electroluminescent Devices

Aromatic imide derivatives play a critical role in boosting the electroluminescent (EL) performance of organic light-emitting diodes (OLEDs). However, the majority of aromatic imide-based materials are limited to long wavelength emission OLEDs rather than blue emissions due to their strong electron-withdrawing characteristics. Herein, two novel polycyclic fused amide units were reported as electron acceptor to be combined with either a tetramethylcarbazole or acridine donor via a phenyl linker to generate four conventional fluorescence blue emitters of BBI-4MeCz, BBI-DMAC, BSQ-4MeCz and BSQ-DMAC for the first time. BSQ-4MeCz and BSQ-DMAC based on a BSQ unit exhibited higher thermal stability and photoluminescence quantum yields than BBI-4MeCz and BBI-DMAC based on a BBI unit due to their more planar acceptor structure. The intermolecular interactions that exist in the BSQ series materials effectively inhibit the molecular rotation and configuration relaxation, and thus allow for blue-shifted emissions. Blue OLED devices were constructed with the developed materials as emitters, and the effects of both the structure of the polycyclic fused amide acceptor and the electron donor on the EL performance were clarified. Consequently, a sky-blue OLED device based on BSQ-DMAC was created, with a high maximum external quantum efficiency of 4.94% and a maximum luminance of 7761 cd m⁻².

Collective Synthesis of Illudalane Sesquiterpenes via Cascade Inverse Electron Demand (4 + 2) Cycloadditions of Thiophene S,S-Dioxides

Thiophene S,S-dioxides are underutilized tools for the de novo construction of benzene rings in organic synthesis. We report a collective synthesis of nine illudalane sesquiterpenes using bicyclic thiophene S,S-dioxides as generalized precursors to the indane core of the natural products. Exploiting furans as unusual dienophiles in this inverse electron demand Diels-Alder cascade, this concise and convergent approach enables the synthesis of these targets in as little as five steps. Theoretical studies rationalize the reactivity of thiophene S,S-dioxides with both electron-poor and electron-rich dienophiles and reveal reaction pathways involving either nonpolar pericyclic or bifurcating ambimodal cycloadditions. Overall, this work demonstrates the wider potential of thiophene S,S-dioxides as convenient and flexible precursors to polysubstituted arenes.

A Calix[3]acridan-Based Host-Guest Cocrystal Exhibiting Efficient Thermally Activated Delayed Fluorescence

A supramolecular strategy to construct thermally activated delayed fluorescence (TADF) materials through host-guest charge transfer interactions was proposed. Consequently, a new class of macrocycle namely calix[3]acridan was conveniently synthesized in 90 % yield. The host-guest cocrystal formed by calix[3]acridan and 1,2-dicyanobenzene exhibited efficient TADF properties due to intense intermolecular charge transfer interactions. Moreover, the spatially separated highest occupied molecular orbital and lowest unoccupied molecular orbital resulted in a very small singlet-triplet energy gap of 0.014 eV and hence guaranteed an efficient reverse intersystem crossing for TADF. Especially, a high photoluminescence quantum yield of 70 % was achieved, and it represents the highest value among the reported intermolecular donor-acceptor TADF materials.

Advances in circularly polarized electroluminescence based on chiral TADF-active materials

This review summarizes the development status of chiral TADF-active materials with CPEL, covering chiral perturbed TADF molecules, intrinsically chiral TADF molecules, and TADFsensitized fluorescent enantiomers.

Theoretical studies on boron dimesityl-based thermally activated delayed fluorescence organic emitters: excited-state properties and mechanisms

At 300 K, S1 excitons could emit fluorescence or undergo ISC to T1, where rISC exceeds the phosphorescence emission enabling TADF.

Tandem rigidification and π-extension as a key tool for the development of a narrow linewidth yellow hyperfluorescent OLED system

Hyperfluorescence (HF), a relatively new phenomenon utilizing the transfer of excitons between two luminophores, requires careful pairwise tuning of molecular energy levels and is proposed to be the crucial step towards the development of new, highly effective OLED systems. To date, barely few HF yellow emitters with desired narrowband emission but moderate external quantum efficiency (EQE < 20%) have been reported. This is because a systematic strategy embracing both Förster resonance energy transfer (FRET) and triplet to singlet (TTS) transition as complementary mechanisms for effective exciton transfer has not yet been proposed. Herein, we present a rational approach, which allows, through subtle structural modification, a pair of compounds built from the same donor and acceptor subunits, but with varied communication between these ambipolar fragments, to be obtained. The TADF-active dopant is based on a naphthalimide scaffold linked to the nitrogen of a carbazole moiety, which through the introduction of an additional bond leads not only to π-cloud enlargement, but also rigidifies and inhibits the rotation of the donor. This structural change prevents TADF, and guides bandgaps and excited state energies to simultaneously pursue FRET and TTS processes. New OLED devices utilizing the presented emitters show excellent external quantum efficiency (up to 27%) and a narrow full width at half maximum (40 nm), which is a consequence of very good alignment of energy levels. The presented design principles prove that only a minor structural modification is needed to obtain commercially applicable dyes for HF OLED devices.

The rigidification with simultaneous π-extension of TADF-active dye leads to fluorescent dopant with fine-tuned energy levels. These used as hyperfluorescent OLED device shows extraordinary EQE and brightness due to effective FRET and TTS processes.

TADF-Sensitized Fluorescent Enantiomers: A New Strategy for High-Efficiency Circularly Polarized Electroluminescence*

A promising strategy of thermally activated delayed fluorescence (TADF) sensitized circularly polarized luminescence (CPL) has been proposed for improving the electroluminescence efficiencies of circularly polarized fluorescent emitters. Compared with chiral TADF emitters which suffer from the dilemma of small ΔE_ST accompanied by small k_r , the TADF-sensitized CPL (TSCP) strategy using TADF molecules as sensitizers and CP-FL molecules as emitters might be the most promising method to construct high-performance circularly polarized organic light-emitting diodes (CP-OLEDs). Consequently, by taking advantage of the theoretically 100 % exciton utilization of TADF sensitizers, especially, by designing CP-FL emitters with high PLQY, narrow FWHM and large g_lum values, TSCP-type CP-OLEDs with excellent overall performances can be realized.

High-Efficiency Circularly Polarized Electroluminescence from TADF-Sensitized Fluorescent Enantiomers

A couple of fluorescent enantiomers, which are suitable for the emitters of high-efficiency TADF-sensitized CP-OLEDs, have been developed. The enantiomers show configurational stability, high PLQY of 98 %, large k_r of 7.8×10⁷  s^-1 , and intense CPL activities with |g_lum | values of about 2.5×10^-3 . Notably, by using matchable TADF sensitizer, the enantiomers were then exploited as emitter to fabricate CP-OLEDs. The TADF-sensitized CP-OLEDs not only show mirror-image CPEL activities with g_EL values of +1.8×10^-3 and -1.4×10^-3 , but also display fast start-up featuring with low V_T of 3.0 V as well as driving voltage of 4.8 V at 10 000 cd m^-2 . Meaningfully, the TADF-sensitized fluorescent devices show high EQE_max of 21.5 % and extremely low efficiency roll-off, whose EQEs are 21.2 % and 15.3 % at 1000 and 10 000 cd m^-2 , respectively. The obtained EQEs are comparable to those of CP-TADF emitters, which provides a promising perspective to break through the EL efficiency limit of CP-FL emitters.

P∩N Bridged Cu(I) Dimers Featuring Both TADF and Phosphorescence. From Overview towards Detailed Case Study of the Excited Singlet and Triplet States

We present an overview over eight brightly luminescent Cu(I) dimers of the type Cu₂X₂(P∩N)₃ with X = Cl, Br, I and P∩N = 2-diphenylphosphino-pyridine (Ph₂Ppy), 2-diphenylphosphino-pyrimidine (Ph₂Ppym), 1-diphenylphosphino-isoquinoline (Ph₂Piqn) including three new crystal structures (Cu₂Br₂(Ph₂Ppy)₃ 1-Br, Cu₂I₂(Ph₂Ppym)₃ 2-I and Cu₂I₂(Ph₂Piqn)₃ 3-I). However, we mainly focus on their photo-luminescence properties. All compounds exhibit combined thermally activated delayed fluorescence (TADF) and phosphorescence at ambient temperature. Emission color, decay time and quantum yield vary over large ranges. For deeper characterization, we select Cu₂I₂(Ph₂Ppy)₃, 1-I, showing a quantum yield of 81%. DFT and SOC-TDDFT calculations provide insight into the electronic structures of the singlet S₁ and triplet T₁ states. Both stem from metal+iodide-to-ligand charge transfer transitions. Evaluation of the emission decay dynamics, measured from 1.2 ≤ T ≤ 300 K, gives ∆E(S₁-T₁) = 380 cm⁻¹ (47 meV), a transition rate of k(S₁→S₀) = 2.25 × 10⁶ s⁻¹ (445 ns), T₁ zero-field splittings, transition rates from the triplet substates and spin-lattice relaxation times. We also discuss the interplay of S₁-TADF and T₁-phosphorescence. The combined emission paths shorten the overall decay time. For OLED applications, utilization of both singlet and triplet harvesting can be highly favorable for improvement of the device performance.

A Brief History of OLEDs-Emitter Development and Industry Milestones

Organic light-emitting diodes (OLEDs) have come a long way ever since their first introduction in 1987 at Eastman Kodak. Today, OLEDs are especially valued in the display and lighting industry for their promising features. As one of the research fields that equally inspires and drives development in academia and industry, OLED device technology has continuously evolved over more than 30 years. OLED devices have come forward based on three generations of emitter materials relying on fluorescence (first generation), phosphorescence (second generation), and thermally activated delayed fluorescence (third generation). Furthermore, research in academia and industry toward the fourth generation of OLEDs is in progress. Excerpts from the history of green, orange-red, and blue OLED emitter development on the side of academia and milestones achieved by key players in the industry are included in this report.

Solid-state effect on luminescent properties of thermally activated delayed fluorescence molecule with aggregation induced emission: A theoretical perspective

Solid-state effect plays an important role in defining the nature of excited states for thermally activated delayed fluorescence (TADF) molecules and further affects their luminescence properties. Theoretical investigation of photophysical properties with explicit consideration of intermolecular interactions in solid phase, is highly desired. In this work, the luminescent properties of new TADF molecule SBF-BP-DMAC with aggregation induced emission (AIE) feature are theoretically studied both in solution and solid phase. Solvent environment effect in Tetrahydrofuran (THF) is simulated by polarizable continuum model (PCM) and solid-state effect is considered by the combined quantum mechanics and molecular mechanics (QM/MM) method. By combing thermal vibration correlation function (TVCF) theory with first principles calculation, excited state energy consumption process is investigated. Our results show that the calculated prompt fluorescence efficiency, delayed fluorescence efficiency and total fluorescence efficiency in THF is 3.0%, 0.4‰ and 3.0% respectively, and corresponding value increases to 14.4%, 31.5% and 45.9% for molecule in solid phase, this verifies the AIE feature. To detect the inner mechanisms, the geometrical structures, Huang-Rhys (HR) factors and reorganization energies as well as excited state transition properties are analyzed. Decreased HR factor and reorganization energy are found in solid phase, this is caused by the restricted torsion motion of DMAC unit in rigid environment. Thus, non-radiative energy consumption process is suppressed and enhanced fluorescence efficiency is found in the solid phase. Moreover, the smaller energy gap between S₁ and T₁ in the solid state than that in THF, is more conducive for reverse intersystem crossing process and further improves the efficiency. This work provides reasonable explanation for the experimental measurements and reveals the inner perspectives for AIE and TADF mechanisms, which is advantageous to develop new non-doped OLEDs with advanced feature.

Circularly Polarized Luminescence in Nanoassemblies: Generation, Amplification, and Application

Currently, the development of circularly polarized luminescent (CPL) materials has drawn extensive attention due to the numerous potential applications in optical data storage, displays, backlights in 3D displays, and so on. While the fabrication of CPL-active materials generally requires chiral luminescent molecules, the introduction of the "self-assembly" concept offers a new perspective in obtaining the CPL-active materials. Following this approach, various self-assembled materials, including organic-, inorganic-, and hybrid systems can be endowed with CPL properties. Benefiting from the advantages of self-assembly, not only chiral molecules, but also achiral species, as well as inorganic nanoparticles have potential to be self-assembled into chiral nanoassemblies showing CPL activity. In addition, the dissymmetry factor, an important parameter of CPL materials, can be enhanced through various pathways of self-assembly. Here, the present status and progress of self-assembled nanomaterials with CPL activity are reviewed. An overview of the key factors in regulating chiral emission materials at the supramolecular level will largely boost their application in multidisciplinary fields.

Dual-Mode Detection of Bacterial 16S Ribosomal RNA in Tissues

The specific detection of pathogens has long been recognized as a vital strategy for controlling bacterial infections. Herein, a novel hydrophilic aromatic-imide-based thermally activated delayed fluorescence (TADF) probe, AI-Cz-Neo, is designed and synthesized by the conjugation of a TADF emitter with a bacterial 16S ribosomal RNA-targeted moiety, neomycin. Biological data showed for the first time that AI-Cz-Neo could be successfully applied for the dual-mode detection of bacterial 16S rRNA using confocal fluorescence imaging and time-resolved fluorescence imaging (TRFI) in both cells and tissues. These findings greatly expand the application of TADF fluorophores in time-resolved biological imaging and provide a promising strategy for the precise and reliable diagnosis of bacterial infections based on the dual-mode imaging of bacterial 16S rRNA by fluorescence intensity and fluorescence lifetime.

Realizing Efficient Single Organic Molecular White Light-Emitting Diodes from Conformational Isomerization of Quinazoline-Based Emitters

Single pure organic molecular white light emitters (SPOMWLEs) are of significance as a new class of material for white lighting applications; however, few of them are able to emit white electroluminescence from organic light-emitting diodes. Herein, donor-π-acceptor conjugated emitters, 2PQ-PTZ and 4PQ-PTZ, were designed and synthesized as SPOMWLEs for white light emission considering the distinct advantages of their conformation isomers. The coexistence of conformational isomers in 2PQ-PTZ, which is the first experimental evidence of the coexisting quasi-axial and quasi-equatorial conformers, provides ideal flexibility to obtain white light emission from their simultaneous and well-separated fluorescence and thermally activated delayed fluorescence. With these remarkable properties, a 2PQ-PTZ-based white light-emitting diode (LED) with a CIE of (0.32, 0.34) and color rendering index (CRI) of 89 is demonstrated. Further, the white organic light-emitting diode (OLED) of 2PQ-PTZ exhibits a high external quantum efficiency (EQE) of 10.1%, which is the reported highest performance among SPOMWLE-based OLEDs.

An axially chiral thermally activated delayed fluorescent emitter with a dual emitting core for a highly efficient organic light-emitting diode

An axially chiral TADF emitter with a dual-emitting-core showed a high PLQY and EQE (20.8%), while its enantiomers also exhibited CPL properties.

Synthesis of polysubstituted arenes through organocatalytic benzannulation

Polysubstituted arenes serve as ubiquitous structural cores of aromatic compounds with significant applications in chemistry, biological science, and materials science. Among all the synthetic approaches toward these highly functionalized arenes, organocatalytic benzannulation represents one of the most efficient and versatile transformations in the assembly of structurally diverse arene architectures under mild conditions with exceptional chemo-, regio- or stereoselectivities. Thus, the development of new benzannulation reactions through organocatalysis has attracted much attention in the past ten years. This review systemically presents recent advances in the organocatalytic benzannulation strategies, categorized as follows: (1) Brønsted acid-catalysis, (2) secondary amine catalysis, (3) primary amine catalysis, (4) tertiary amine catalysis, (5) tertiary phosphine catalysis, and (6) N-heterocyclic carbene catalysis. Each part is further classified into several types according to the number of carbon atoms contributed by different synthons participating in the cyclization reaction. The reaction mechanisms involved in different benzannulation strategies were highlighted.

Organocatalytic benzannulation represents one of the most efficient transformations for assembling polysubstituted arenes, this review presents recent advances in organocatalytic benzannulation strategies to construct functionalized benzenes.

An ultralong room-temperature phosphorescent material based on the combination of small singlet–triplet splitting energy and H-aggregation

Compound AI-N-Cz exhibited ultralong RTP with a lifetime of 775 ms due to the combination of small ΔE_ST and H-aggregation.

A single component self-assembled thermally activated delayed fluorescence nanoprobe

A novel versatile thermally activated delayed fluorescence (TADF) nanoprobe, AI-Cz-NP, was constructed by self-assembly of a single-component amphiphilic monomer for potential applications in confocal imaging and time-resolved fluorescence imaging.

Recent advances in circularly polarized electroluminescence based on organic light-emitting diodes

This review summarizes the recent advances in CP-OLEDs based on chiral conjugated polymers, chiral metal complexes, and chiral simple organic molecules.

Difluoroboron-Enabled Thermally Activated Delayed Fluorescence

A new series of tetracoordinated boron-enabled thermally activated delayed fluorescence (TADF) materials with a donor-acceptor BF₂-type framework were designed and conveniently synthesized. Difluoroboron plays a critical role and acts as a key to coordinate with the latent acceptor of the 2-(4-phenylpyridin-2-yl)phenol (PPyPOH) moiety to realize TADF. TADF materials are air-stable and have a high photoluminescence quantum yield of up to 99%. NOBF2-Cz- and NOBF2-DPCz-doped blue OLEDs demonstrated EQEs of 11.0% with CIE coordinates of (0.14, 0.16) and 15.8% with (0.14, 0.28) and high brightness of 6761 and 19383 cd/m² could be achieved, respectively. Moreover, the blue OLED doped with NOBF2-DPCz and the green OLED doped with NOBF2-DMAC achieved operational lifetimes at 50% of initial luminance (L₀ = 500 cd/m²), LT₅₀, of 54 and 920 h, respectively. This work indicates that these tetracoordinated difluoroboron molecules can act as efficient and stable TADF materials for OLED applications.

Photoactivatable Fluorogenic Labeling via Turn-On "Click-Like" Nitroso-Diene Bioorthogonal Reaction

Fluorogenic labeling enables imaging cellular molecules of interest with minimal background. This process is accompanied with the notable increase of the quantum yield of fluorophore, thus minimizing the background signals from unactivated profluorophores. Herein, the development of a highly efficient and bioorthogonal nitroso-based Diels-Alder fluorogenic reaction is presented and its usefulness is validated as effective and controllable in fluorescent probes and live-cell labeling strategies for dynamic cellular imaging. It is demonstrated that nitroso-based cycloaddition is an efficient fluorogenic labeling tool through experiments of further UV-activatable fluorescent labeling on proteins and live cells. The ability of tuning the fluorescence of labeled proteins by UV-irradiation enables selective activation of proteins of interest in a particular cell compartment at a given time point, while leaving the remaining labeled molecules untouched.