Thermally Activated Delayed Fluorescence Molecules Research Articles

Declined Singletbut Constant TripletEnergy: Thermally Activated Delayed Fluorescence with Triplet Blocking Effect.

Thermally activated delayed fluorescence (TADF) molecules have been widely investigated in organic light emitting diodes, etc. Small singlet-triplet energy gapand high radiative constantsare desired. The prevalent TADF molecules are via donor-acceptor molecular design, whichis at the expense of reducing radiative constants. Herein, we demonstrated a new singlet-triplet energy gap modulation approach to construct TADF with high radiative constant, based on triplet blocking effect, i.e., the extension of conjugation of a triplet constrainer (IB) leads to a gradually red-shifted singletbut a constant tripletenergy, and therefore reduced singlet-triplet energy gap controlled from monomer (IB), monomer-linker (IB-BF2), to dimer of IB-BF2-IB. The natural transition orbital analysis indicates that singletstate is delocalized while tripletstate is localized as confirmed by time resolved electron paramagnetic resonance spectroscopy. Therefore, the singlet-triplet energy gap is reduced from 0.60 eV, 0.46 eV to 0.25 eV, while keeping faster radiation rate (around 10^8/s) than that of conventional donor-acceptor molecules (10^6 ~ 10^7/s). As a result, the emission mechanisms are regulated from fluorescence for IB, phosphorescence/TADF dual emissions for IB-BF2 to TADF for IB-BF2-IB. This paper proposed a new approach of singlet-triplet energy gap modulation, which is crucial for fundamental photophysics and material science.

Rigid and planar π-conjugated molecules leading to long-lived intramolecular charge-transfer states exhibiting thermally activated delayed fluorescence

Intramolecular charge transfer (ICT) occurs when photoexcitation causes electron transfer from an electron donor to an electron acceptor within the same molecule and is usually stabilized by decoupling of the donor and acceptor through an orthogonal twist between them. Thermally activated delayed fluorescence (TADF) exploits such twisted ICT states to harvest triplet excitons in OLEDs. However, the highly twisted conformation of TADF molecules results in limited device lifetimes. Rigid molecules offer increased stability, yet their typical planarity and π-conjugated structures impedes ICT. Herein, we achieve dispersion-free triplet harvesting using fused indolocarbazole-phthalimide molecules that have remarkably stable co-planar ICT states, yielding blue/green-TADF with good photoluminescence quantum yield and small singlet-triplet energy gap < 50 meV. ICT formation is dictated by the bonding connectivity and excited-state conjugation breaking between the donor and acceptor fragments, that stabilises the planar ICT excited state, revealing a new criterion for designing efficient TADF materials.

Understanding Spin-Orbit-Coupling-Induced Reverse Intersystem Crossing in DMAC-TRZ-Doped Organic Light-Emitting Diodes via Magnetic-Field-Effect Measurement.

An efficient reverse intersystem crossing (RISC) process in thermally activated delayed fluorescence (TADF) material is a common way to obtain high-performance organic light-emitting diodes (OLEDs), but the physical mechanism for the spin flipping of the RISC remains vague. Here, using magneto-electroluminescence (MEL) as an effective tool, we found that the RISC (CT3 → CT1) from a triplet charge transfer (CT3) to the singlet charge transfer (CT1) state is decided by spin-orbit coupling (SOC) in metal-free OLEDs based on a typical TADF emitter DMAC-TRZ. By fitting and analyzing the current and concentration-dependent MEL data, it is found that the characteristic magnetic field of the SOC-induced RISC process is approximately 65-85 mT, which is obviously larger than that (several mT) of the hyperfine-interaction-induced RISC process. Simultaneously, the dissociation effect of the electric field on the CT3 state causes the SOC-induced RISC process to decrease with increasing bias current. The different formation methods of excited states lead to the nonmonotonic change of SOC-induced RISC process with the increase of dopant concentration. Furthermore, considering the orbital polarization of dipoles, the SOC mechanism is further verified by the measurement of magneto-photoluminescence to be the responsible for achieving the spin flipping in TADF molecules. Therefore, this work clarifies the underlying dynamic mechanism of the RISC process in TADF-OLEDs.

Regulation of TADF and RTP Dual Emission via Internal and External Heavy-Atom Effects.

Organic materials with thermally activated delayed fluorescence (TADF) and room-temperature phosphorescence (RTP) dual emission have attracted great attention in recent years, but the regulation mechanism via internal and external heavy atoms is not clear enough. Here, we carry out a systematic theoretical investigation on the photophysical properties of the materials by introducing aliphatic or aromatic bromine atoms. The molecule with aromatic bromine atoms exhibits obvious TADF owing to the effective reverse intersystem crossing (RISC) with matchable energy levels and enhanced spin orbit couplings, the molecule with aliphatic bromine atoms shows a long RTP lifetime because of the reduced nonradiative transition of triplet excitons, and the molecule with both aliphatic and aromatic bromine atoms presents balanced TADF and RTP emissions thanks to the synergy internal and external heavy-atom effects. Besides, the internal and external heavy atoms induce multisite intermolecular interactions, effectively suppressing the nonradiative process in the solid phase. The efficient RISC process and the suppressed nonradiative process of triplet excitons should be key to regulating the dual emission property. These findings and insights are of great importance for revealing the structure-performance relationship, providing theoretical guidance for the design of TADF and RTP dual emission molecules via internal and external heavy-atom effects.

Donor-only substituted benzene achieves thermally activated delayed fluorescence

Thermally activated delayed fluorescence (TADF) is a promising mechanism for harvesting triplet excitons in organic light-emitting diodes (OLEDs). The donor–acceptor (D–A) design is the most conventional strategy for developing efficient TADF emitters. A subsequently emerged approach, known as the multiple resonance (MR) effect, also employs electron-donating and electron-withdrawing functional groups. Thus, developing TADF materials has traditionally relied on ingenuity in selecting and combining two functional units. Here, we have realized a TADF molecule by utilizing only a carbazole donor moiety. This molecule is an unusual example in the family of TADF materials and offers better insight into the electronic structures in the excited states for luminescent materials.

Efficient thermally activated delayed fluorescence materials from symmetric anthraquinone derivatives for high-performance red OLEDs

Constructing efficient red thermally activated delayed-fluorescence (TADF) materials for high-performance organic light-emitting diodes (OLEDs) remains challenging due to the formidable barrier of energy gap law. In this work, a design strategy of connecting two donor units to the adjacent positions of electron acceptor is proposed for creating red luminescent materials, and four Y-shaped TADF molecules consisting of strong electron-withdrawing anthraquinone (AQ) acceptor and triphenylamine or acridine-based donors are designed and synthesized. They exhibit strong red emissions (604−618 nm) in toluene solutions and orange/red emissions (566−608 nm) with good photoluminescence quantum yields (43−68%) in doped films, and enjoy small singlet-triplet energy gaps (0.02−0.10 eV) and fast reverse intersystem crossing processes (1.5–7.3 × 105 s−1), which are attributed to the unique Y-shape structure. A maximum external quantum efficiency of 19.5% with an electroluminescence peak at 616 nm is achieved for AQ-PTPA-based red doped device, representing the highest level for red TADF-OLEDs based on AQ acceptor in the literature. This work can provide guidance for the design of efficient red delayed-fluorescence molecules for the application in OLEDs.

Design of Thermally Activated Delayed Fluorescence Materials: Transition from Carbonyl to Amide‐Based Acceptor

AbstractBenzophenone skeletons containing a carbonyl unit (O=C) have been widely used as electron acceptors in the thermally activated delayed fluorescence (TADF) materials. Herein, we present a novel molecular design concept for TADF materials by transitioning from a carbonyl to an amide (O=C−N) skeleton as the acceptor. The amide unit, compared to its carbonyl counterpart, offers a more stable electronic configuration. Leveraging this insight, we have developed a series of high‐performance TADF molecules based on benzoyl carbazole and carbazoline acceptors. These molecules exhibit exceptionally small singlet‐triplet energy gaps and pronounced aggregation‐enhanced emission properties, achieving photoluminescence quantum yields in neat films as high as 99 %. Consequently, these materials serve as efficient emitters in non‐doped organic light‐eimtting diodes (OLEDs), reaching a maximum quantum efficiency (EQEmax) of up to 26.0 %, significantly higher than the 17.0 % obtained with benzophenone acceptor‐based TADF molecules. Additionally, they have been used as TADF hosts in narrowband red fluorescent OLEDs, setting a record‐high EQEmax of 22.4 %.

Design of Thermally Activated Delayed Fluorescence Materials: Transition from Carbonyl to Amide-Based Acceptor.

Benzophenone skeletons containing a carbonyl unit (O=C) have been widely used as electron acceptors in the thermally activated delayed fluorescence (TADF) materials. Herein, we present a novel molecular design concept for TADF materials by transitioning from a carbonyl to an amide (O=C-N) skeleton as the acceptor. The amide unit, compared to its carbonyl counterpart, offers a more stable electronic configuration. Leveraging this insight, we have developed a series of high-performance TADF molecules based on benzoyl carbazole and carbazoline acceptors. These molecules exhibit exceptionally small singlet-triplet energy gaps and pronounced aggregation-enhanced emission properties, achieving photoluminescence quantum yields in neat films as high as 99 %. Consequently, these materials serve as efficient emitters in non-doped organic light-eimtting diodes (OLEDs), reaching a maximum quantum efficiency (EQEmax) of up to 26.0 %, significantly higher than the 17.0 % obtained with benzophenone acceptor-based TADF molecules. Additionally, they have been used as TADF hosts in narrowband red fluorescent OLEDs, setting a record-high EQEmax of 22.4 %.

Thermally Activated Delayed Fluorescence and Beyond. Photophysics and Material Design Strategies.

This review focuses on thermally activated delayed fluorescence (TADF). Photophysical properties of Cu(I) complexes and unique organic molecules are addressed. Investigations, based on temperature‐dependent emission studies, micro‐ to femto‐second time‐resolved spectroscopy investigations, quantum mechanical considerations, state‐of‐art calculations, and organic light‐emitting diodes (OLED) device studies, address exciton harvesting mechanisms and photophysical impact of the energy gap ΔE(S1–T1) and spin‐orbit coupling (SOC). We disclose relationship between (i) ΔE(S1–T1) and transition rate k(S1–S0); (ii) SOC, phosphorescence, and intersystem crossing (ISC); (iii) internal/external rigidity, luminescence quantum yield, excitation self‐trapping, and concentration quenching; (iv) environment polarity and state energy tuning, as well as (v) SOC and combined ambient‐temperature TADF/phosphorescence, zero‐field splitting, and spin‐lattice relaxation (at T = 1.2 K). These studies guide us to milestone Cu(I) complexes. Moreover, we demonstrate that fast ISC in organic molecules requires state mixing with an additional, energetically close triplet state. Thus, a guide structure for unique organic TADF molecules with ultra‐fast ISC and reverse‐ISC rates (&gt;109 s−1) combined with ΔE(S1–T1)&lt;10 cm−1 (&lt;1 meV) is presented allowing for ultra‐fast singlet‐triplet equilibrated fluorescence with sub‐microsecond decay. First OLEDs fabricated show high external quantum efficiency of ≈19%. Based on this breakthrough material class, a new exciton harvesting mechanism, the direct singlet harvesting (DSH), is presented.

Boron cluster-based TADF emitter via through-space charge transfer enabling efficient orange-red electroluminescence

Thermally activated delayed fluorescence (TADF) materials driven by a through-space charge transfer (TSCT) mechanism have garnered wide interest. However, access of TSCT-TADF molecules with long-wavelength emission remains a formidable challenge. In this study, we introduce a novel V-type D-A-D-A' emitter, Trz-mCzCbCz, by using a carborane scaffold. This design strategically incorporates carbazole (Cz) and 2,4,6-triphenyl-1,3,5-triazine (Trz) as donor and acceptor moieties, respectively. Theoretical calculations alongside experimental validations affirm the typical TSCT-TADF characteristics of this luminogen. Owing to the unique structural and electronic attributes of carboranes, Trz-mCzCbCz exhibits an orange-red emission, markedly diverging from the traditional blue-to-green emissions observed in classical Cz and Trz-based TADF molecules. Moreover, bright emission in aggregates was observed for Trz-mCzCbCz with absolute photoluminescence quantum yield (PLQY) of up to 88.8%. As such, we have successfully fabricated five organic light-emitting diodes (OLEDs) by utilizing Trz-mCzCbCz as the emitting layer. It is important to note that both the reverse intersystem crossing process and the TADF properties are profoundly influenced by host materials. The fabricated OLED devices reached a maximum external quantum efficiency (EQE) of 12.7%, with an emission peak at 592 nm. This represents the highest recorded efficiency for TSCT-TADF OLEDs employing carborane derivatives as emitting layers.

Reverse Intersystem Crossing Boosting Sensitizer for Ultra-High Efficiency Blue Organic Light-Emitting Diode.

In designing thermally activated delayed fluorescence (TADF) emitters, a high reverse intersystem crossing (RISC) rate with a high photoluminescence quantum yield is essential. Herein, two blue TADF molecules, 2',5'-di(9H-carbazol-9-yl)-3',6'-bis(3,6-ditert-butyl-9H-carbazol-9-yl)-[1,1':4',1″-terphenyl]-4,4″-dicarbonitrile (CzTCzPhBN) and 2',5'-bis(3,6-ditert-butyl-9H-carbazol-9-yl)-3',6'-bis(3,6-diphenyl-9H-carbazol-9-yl)-[1,1':4',1″-terphenyl]-4,4″-dicarbonitrile (PhCzTCzPhBN) with a high RISC rate, were developed through donor engineering. CzTCzPhBN and PhCzTCzPhBN showed a high RISC rate of 4.00 × 105 and 16.62 × 105 s-1, respectively, with a high photoluminescence quantum yield of 80.1 and 84.9%, which resulted in high external quantum efficiency of 27.0 and 27.8% with color coordinates (0.148, 0.170) and (0.150, 0.230) in blue TADF organic light-emitting diodes, respectively. The high RISC rate and device efficiency inspired two TADF molecules to be used as sensitizers in hyperfluorescence devices. The hyperfluorescence devices showed ultra-high external quantum efficiency of 30.7 and 36.4% with color coordinates (0.125, 0.164) and (0.127, 0.193), respectively.

Visualization of Multiple-Resonance-Induced Frontier Molecular Orbitals in a Single Multiple-Resonance Thermally Activated Delayed Fluorescence Molecule.

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

Multireference Ab Initio Calculations on Excited Electronic States of Carbazole-Based Organic Compounds for Thermally Activated Delayed Fluorescence.

The emerging technology of organic light-emitting diodes takes advantage of the thermally activated delayed fluorescence (TADF) mechanism for improved efficiency. Carbazole-based organic molecules are suitable for TADF emission because of charge transfer excitations between the electron-donor carbazole and an electron-acceptor unit. Computational design of new TADF molecules with the desired properties is challenging because charge-transfer excitations cannot be predicted accurately by time-dependent density functional theory. Four groups of carbazole-based donor-acceptor molecules have been studied using multireference ab initio methods to understand the nature of excited electronic states. The state-averaged complete active space self-consistent field (SA-CASSCF) and the N-electron valence state perturbation theory (NEVPT2) were used to calculate energies and oscillator strengths for multiple excited electronic states. The number of active electrons and orbitals and the number of excited states included in state-averaged CASSCF were selected such that the accuracy of ab initio predictions could be improved systematically. The procedure introduced here for the calculation of multiple excited electronic states of TADF candidates can be used to accelerate the computational search for efficient TADF materials.

Excited-State Engineering Enables Efficient Deep-Blue Light-Emitting Diodes Exhibiting BT.2020 Color Gamut.

Organic luminescent materials that exhibit thermally activated delayed fluorescence (TADF) can convert non-emissive triplet excitons into emissive singlet states through a reverse intersystem crossing (RISC) process. Therefore, they have tremendous potential for applications in organic light-emitting diodes (OLEDs). However, with the development of ultra-high definition 4K/8K display technologies, designing efficient deep-blue TADF materials to achieve the Commission Internationale de l'Éclairage (CIE) coordinates fulfilling BT.2020 remains a significant challenge. Here, an effective approach is proposed to design deep-blue TADF molecules based on hybrid long- and short-range charge-transfer by incorporation of multiple donor moieties into organoboron multiple resonance acceptors. The resulting TADF molecule exhibits deep-blue emission at 414nm with a full width at half maximum (FWHM) of 29nm, together with a thousand-fold increase in RISC rate. OLEDs based on the champion material achieve a record maximum external quantum efficiency (EQE) of 22.8% with CIE coordinates of (0.163, 0.046), approaching the coordinates of the BT.2020 blue standard. Moreover, TADF-assisted fluorescence devices employing the designed material as a sensitizer exhibit an exceptional EQE of 33.1%. This work thus provides a blueprint for future development of efficient deep-blue TADF emitters, representing an important milestone towards meeting the blue color gamut standard of BT.2020.

Theoretical insights on highly efficient X-shaped near-infrared thermal activation delayed fluorescence emitter

The near-infrared (NIR) thermally activated delayed fluorescence (TADF) molecules hold practical application value in various fields, including biological imaging, anti-counterfeiting, sensors, telemedicine, photomicrography, and night vision display. These molecules have emerged as a significant development direction in organic electroluminescent devices, offering exciting possibilities for future technological advancements. Despite the remarkable potential of NIR-TADF molecules in various applications, the development of molecules that exhibit both long-wavelength emission and high efficiency remains a significant challenge. Herein, based on T-type and Y-type TADF molecules BCN-TPA and ECN-TPA, a novel X-type TADF molecule X-ECN-TPA is theoretically designed through a molecular fusion strategy. Utilizing first-principles calculations and the thermal vibration correlation function (TVCF) method, the photophysical properties and luminescent mechanisms of these three molecules in both solvent and solid (doped films) are revealed. A comparison of the luminescent properties of isomeric BCN-TPA and ECN-TPA shows that the enhanced luminescence efficiency of BCN-TPA in the solid states is attributed to higher radiative rates and lower non-radiative rates. Furthermore, compared to BCN-TPA and ECN-TPA, X-ECN-TPA exhibits significant conjugation extension, resulting in a pronounced redshift, reaching 831 nm and 813 nm in solvent and solid states, respectively. Importantly, molecular fusion significantly increases the transition dipole moment density between the donor and acceptor, leading to a substantial increase in radiative transition rates. Additionally, molecular fusion effectively reduces the energy gap between the first singlet excited state (S1) and the first triplet excited state (T1), facilitating the improvement of the reverse intersystem crossing (RISC) process. In addition, the calculation of Marcus formula shows that the triplet energy transfer from CBP to BCN-TPA, ECN-TPA and X-ECN-TPA is very effective. This work not only designs a novel efficient NIR-TADF molecule but also proposes a strategy for designing efficient NIR-TADF molecules. This principle offers unique insights for optimizing traditional molecular frameworks, opening up new possibilities for future advancements.

Introducing Internal Host Component to Thermally Activated Delayed Fluorescence Emitter for Efficient NIR Nondoped Organic Light-Emitting Diodes.

Developing thermally activated delayed fluorescence (TADF) near-infrared (NIR) organic light-emitting diodes (OLEDs) based on nondoped emitting layers is intriguing yet challenging, limited by low exciton utilization and notorious concentration quenching. Herein, a facile strategy is proposed to address this issue by incorporating an internal host component onto a traditional donor (D)-acceptor (A)-type red TADF molecule. A proof-of-concept emitter with an internal host is accordingly developed as well as a control one without an internal host. In the case of their monomer states, both emitters exhibit similar emission spectra due to their identical D-A pairs. However, under nondoped conditions, significant improvement in exciton utilization and quenching-resistant features are observed for the molecule with the internal host. The corresponding nondoped OLED yielded a maximum external quantum efficiency of 2.4%, with NIR emission peaking at 765 nm, which was a nearly 10-fold improvement relative to the efficiency based on the control molecule without an internal host. To the best of our knowledge, this result is on par with those of state-of-the art nondoped NIR TADF OLEDs in a similar emission region. These results offer a feasible pathway for the design and development of high-efficiency NIR nondoped OLEDs.

Fine tuning of excited states by trifluoromethylphenyl for blue-shifted color and enhanced EQEs in thermally activated delayed fluorescence emitters

3,6-di-tert-butyl-9H-carbazole and 3,6-diphenyl-9H-carbazole have been widely used to construct blue thermally activated delayed fluorescence (TADF) emitters. However, it is difficult for related emitters to achieve maximum external quantum efficiency (EQEmax) above 20 % with the Commission Internationale de l'Eclairage (CIE) y ≤ 0.12. A new type of donor was developed to construct blue TADF molecules, namely CF3P-BuCz-TRZ and CF3P-PhCz-TRZ. The weak electron-withdrawing trifluoromethylphenyl (CF3P) with moderate steric hindrance was introduced into the 1-site of carbazole donor for improving the color purity for blue TADF emitters. More importantly, the introduction of CF3P tightly compacts the energy levels for the significant excited states in RISC process. The energy gap between the lowest singlet excited (S1) state and the lowest triplet (T1) state (Δ E(S1−T1)), as well as between T1 and the higher triplet (Tn, n ≥ 2) states (Δ E(Tn−T1)) were reduced, so that Tn (n ≥ 2) could be effectively harvested to further promote reverse intersystem crossing (RISC). As a result, the OLEDs based on CF3P-BuCz-TRZ and CF3P-PhCz-TRZ displayed blue electroluminescence with CIE coordinates of (0.156, 0.107) and (0.155, 0.115). In particular, the maximum EQEs of the CF3P-PhCz-TRZ device reached 20.43 % without employing any light out-coupling enhancement or TADF-sensitized structure. This strategy should be valuable for designing more pure-blue and deep-blue TADF emitters.

Inkjet Printing of High-Color-Purity Blue Organic Light-Emitting Diodes with Host-Free Inks.

Inkjet printing technology offers a unique approach to producing direct-patterned pixels without fine metal masks for active matrix displays. Organic light-emitting diodes (OLEDs) consisting of thermally activated delayed fluorescence (TADF) emitters facilitate efficient light emission without heavy metals, such as platinum and iridium. Multi-resonance TADF molecules, characterized by their small full width at half maxima (FWHM), are highly suitable for the requirements of wide color-gamut displays. Herein, host-free TADF inks with a low concentration of 1 mg/mL were developed and inkjet-printed onto a seeding layer, concurrently serving as the hole-transporting layer. Attributed to the proof-of-concept of host-free inks printed on a mixed seeding layer, a maximum external quantum efficiency of 13.1% (improved by a factor of 21.8) was achieved in the inkjet-printed OLED, with a remarkably narrow FWHM of only 32 nm. Highly efficient energy transfer was facilitated by the effective dispersion of the sensitizer around the terminal emitters.

Effective donor and acceptor modifications of carbazole-benzonitrile thermally activated delayed fluorescence molecules enabling high-performance OLEDs

Carbazole-benzonitrile derivatives (CzBNs) have great potential to enable thermally activated delayed fluorescence (TADF) molecules with both high efficiency and good stability simultaneously. However, the device performances of most CzBN-based organic light-emitting diodes (OLEDs) still lag behind other types of TADF molecules. In this work, we proposed a design strategy to construct efficient CzBN-TADF molecules through acceptor and donor modifications. The cyano-modified acceptor enables the extension of the lowest unoccupied molecular orbital while mostly preserving the overlapped area with the highest occupied molecular orbital. The optimized distributions of frontier molecular orbitals contribute to tiny singlet-triplet energy gaps while maintaining a high radiative decay rate. The incorporation of tert-butyl units in the donor groups further enhances the TADF property of resulted tPCNBN molecule due to suppressed non-radiative decay and reduced exciton self-quenching. Accordingly, OLEDs based on tPCNBN present the best device performances, such as a maximum external quantum efficiency of 33.1 % at 400 cd m−2, which is still as high as 26.3 % at a high luminance of 4000 cd m−2, demonstrating relatively low efficiency roll-off. These results confirm the effectiveness of the proposed design strategy in developing efficient and stable CzBN-TADF materials and devices.

Regulation for photophysical properties of thermally activated delayed fluorescence molecules with through-space charge transfer by substitution effect

Thermally activated delayed fluorescence (TADF) molecules with through-space charge transfer (TSCT) have attracted much attention in recent years. The photophysical properties of four TADF molecules with TSCT properties were studied in toluene and in solid phase. Our calculation results indicate that ortho substitution and fluorine substitution not only favor the generation of TADF, but also promote room temperature phosphorescence in solid phase. The results provide deeper understanding of substitution effect on light-emitting properties of TSCT-TADF emitters and may favor the design of TADF emitters.