Thermally Activated Delayed Fluorescence with Nanosecond Emission Lifetimes and Minor Concentration Quenching: Achieving High-Performance Nondoped and Doped Blue OLEDs.

Simultaneously achieving a high photoluminescence quantum yield (PLQY), ultrashort exciton lifetime, and suppressed concentration quenching in thermally activated delayed fluorescence (TADF) materials is desirable yet challenging. Here, a novel acceptor-donor-acceptor type TADF emitter, namely, 2BO-sQA, wherein two oxygen-bridged triarylboron (BO) acceptors are arranged with cofacial alignment and positioned nearly orthogonal to the rigid dispirofluorene-quinolinoacridine (sQA) donor is reported. This molecular design enables the compound to achieve highly efficient (PLQYs up to 99%) and short-lived (nanosecond-scale) blue TADF with effectively suppressed concentration quenching in films. Consequently, the doped organic light-emitting diodes (OLEDs) base on 2BO-sQA achieve exceptional electroluminescence performance across a broad range of doping concentrations, maintaining maximum external quantum efficiencies (EQEs) at over 30% for doping concentrations ranging from 10 to 70 wt%. Remarkably, the nondoped blue OLED achieves a record-high maximum EQE of 26.6% with a small efficiency roll-off of 14.0% at 1000 candelas per square meter. By using 2BO-sQA as the sensitizer for the multiresonance TADF emitter ν-DABNA, TADF-sensitized fluorescence OLEDs achieve high-efficiency deep-blue emission. These results demonstrate the feasibility of this molecular design in developing TADF emitters with high efficiency, ultrashort exciton lifetime, and minimal concentration quenching.

Excellent Charge Separation of NCQDs/ZnS Nanocomposites for the Promotion of Photocatalytic H2 Evolution.

Carbon Quantum dots (CQDs) are widely studied because of their good optical and electronic characteristics and because they can easily generate photocarriers. Nitrogen-doped CQDs (NCQDs) may exhibit improved hydrophilic, optical, and electron-transfer properties, which are conducive to photocatalytic hydrogen evolution. In this paper, NCQD-modified ZnS catalysts were successfully prepared. Under the irradiation of the full spectrum, the H2 evolution rate of the optimal catalyst 0.25 wt % NCQDs/ZnS achieves 5.70 mmol g-1 h-1, which is 11.88, 43.84, and 5.14 times the values of ZnS (0.48 mmol g-1 h-1), NCQDs (0.13 mmol g-1 h-1), and CQDs/ZnS (1.11 mmol g-1 h-1), respectively. Furthermore, it shows good stability, indicating that the modification of NCQDs prevents the photocorrosion and oxidation of ZnS. The enhanced performance is due to NCQD loading, which promotes the separation of photogenerated carriers, optimizes the structures, and increases the specific surface area. This work highlights the fact that NCQD-modified ZnS may afford a new strategy to synthesize ZnS-based photocatalysts with enhanced H2 production performance.

Enhancing Reverse Intersystem Crossing in Triptycene-TADF Emitters: Theoretical Insights into Reorganization Energy and Heavy Atom Effects.

Thermally activated delayed fluorescence (TADF) emitters based on the triptycene skeleton demonstrate exceptional performance, superior stability, and low efficiency roll-off. Understanding the interplay between the luminescent properties of triptycene-TADF molecules and their assembly environments, along with their excited-state characteristics, necessitates a comprehensive theoretical exploration. Herein, we predict the photophysical properties of triptycene-TADF molecules in a thin film environment using the quantum mechanics/molecular mechanics method and quantify their substantial dependency on the heavy atom effects and reorganization energies using the Marcus-Levich theory. Our calculated photophysical properties for two recently reported molecules closely align with experimental values. We design three novel triptycene-TADF molecules by incorporating chalcogen elements (O, S, and Se) to modify the acceptor units. These newly designed molecules exhibit reduced reorganization energies and enhanced reverse intersystem crossing (RISC) rates. The heavy atom effect amplifies spin-orbit coupling, thereby facilitating the RISC process, particularly at a remarkably high rate of ∼109 s-1.

Rotational isomerization: spontaneous structural transformation of a thermally activated delayed fluorescence binuclear copper(I) complex.

A novel binuclear Cu(I) halide complex, Cu2I2(DPPCz)2, which emits efficient thermally activated delayed fluorescence (TADF), is reported. The crystal of this complex spontaneously undergoes ligand rotation and coordination-configuration transformation, converting to its isomer without any external stimulation.

Efficient photocatalytic hydrogen production by space separation of photo-generated charges from S-scheme ZnIn2S4/ZnO heterojunction.

ZnIn2S4/ZnO heterostructures have been achieved by a simple in-situ growth solvothermal method. Under full spectrum irradiation, the optimal photocatalyst 2ZnIn2S4/ZnO exhibits H2 evolution rate of 13,638 (water/ethanol = 1:1) and 3036 (water) µmol·g-1h-1, which is respectively 4 and 5 times higher than that of pure ZnIn2S4. In situ illumination X-ray photoelectron spectroscopy (ISI-XPS) analysis and density functional theory (DFT) calculations show that the electrons of ZnIn2S4 are removed to ZnO through hybridization and form an internal electric field between ZnIn2S4 and ZnO. The optical properties of the catalyst and the effect of internal electric field (IEF) can increase photo-generated electrons (e-)-holes (h+) transport rate and enhance light collection, resulting in profitable photocatalytic properties. The photoelectrochemical and EPR results show that a stepped (S-scheme) heterojunction is formed in the ZnIn2S4/ZnO redox center, which greatly promotes separation of e--h+ pairs and efficient H2 evolution. This research offers an effective method for constructing an efficient S-Scheme photocatalytic system for H2 evolution.

Rational Design of Highly Efficient Orange-Red/Red Thermally Activated Delayed Fluorescence Emitters with Submicrosecond Emission Lifetimes.

The development of orange-red/red thermally activated delayed fluorescence (TADF) materials with both high emission efficiencies and short lifetimes is highly desirable for electroluminescence (EL) applications, but remains a formidable challenge owing to the strict molecular design principles. Herein, two new orange-red/red TADF emitters, namely AC-PCNCF3 and TAC-PCNCF3, composed of pyridine-3,5-dicarbonitrile-derived electron-acceptor (PCNCF3) and acridine electron-donors (AC/TAC) are developed. These emitters in doped films exhibit excellent photophysical properties, including high photoluminescence quantum yields of up to 0.91, tiny singlet-triplet energy gaps of 0.01 eV, and ultrashort TADF lifetimes of less than 1 µs. The TADF-organic light-emitting diodes employing the AC-PCNCF3 as emitter achieve orange-red and red EL with high external quantum efficiencies of up to 25.0% and nearly 20% at doping concentrations of 5 and 40 wt%, respectively, both accompanied by well-suppressed efficiency roll-offs. This work provides an efficient molecular design strategy for developing high-performance red TADF materials.

Realizing High-Efficiency Orange-Red Thermally Activated Delayed Fluorescence Materials through the Construction of Intramolecular Noncovalent Interactions.

The development of highly efficient orange and red thermally activated delayed fluorescence (TADF) materials for constructing full-color and white organic light-emitting diodes (OLEDs) remains insufficient because of the formidable challenges in molecular design, such as the severe radiationless decay and the intrinsic trade-off between the efficiencies of radiative decay and reverse intersystem crossing (RISC). Herein, we design two high-efficiency orange and orange-red TADF molecules by constructing intermolecular noncovalent interactions. This strategy could not only ensure high emission efficiency via suppression of the nonradiative relaxation and enhancement of the radiative transition but also create intermediate triplet excited states to ensure the RISC process. Both emitters exhibit typical TADF characteristics, with a fast radiative rate and a low nonradiative rate. Photoluminescence quantum yields (PLQYs) of the orange (TPA-PT) and orange-red (DMAC-PT) materials reach up to 94 and 87%, respectively. Benefiting from the excellent photophysical properties and stability, OLEDs based on these TADF emitters realize orange to orange-red electroluminescence with high external quantum efficiencies reaching 26.2%. The current study demonstrates that the introduction of intermolecular noncovalent interactions is a feasible strategy for designing highly efficient orange to red TADF materials.

Tröger's Base-Derived Thermally Activated Delayed Fluorescence Dopant for Efficient Deep-Blue Organic Light-Emitting Diodes.

The development of efficient deep-blue emitters with thermally activated delayed fluorescence (TADF) properties is a highly significant but challenging task in the field of organic light-emitting diode (OLED) applications. Herein, we report the design and synthesis of two new 4,10-dimethyl-6H,12H-5,11-methanodibenzo[b,f][1,5]diazocine (TB)-derived TADF emitters, TB-BP-DMAC and TB-DMAC, which feature distinct benzophenone (BP)-derived acceptors but share the same dimethylacridin (DMAC) donors. Our comparative study reveals that the amide acceptor in TB-DMAC exhibits a significantly weaker electron-withdrawing ability in comparison to that of the typical benzophenone acceptor employed in TB-BP-DMAC. This disparity not only causes a noticeable blue shift in the emission from green to deep blue but also enhances the emission efficiency and the reverse intersystem crossing (RISC) process. As a result, TB-DMAC emits efficient deep-blue delay fluorescence with a photoluminescence quantum yield (PLQY) of 50.4% and a short lifetime of 2.28 µs in doped film. The doped and non-doped OLEDs based on TB-DMAC display efficient deep-blue electroluminescence with spectral peaks at 449 and 453 nm and maximum external quantum efficiencies (EQEs) of 6.1% and 5.7%, respectively. These findings indicate that substituted amide acceptors are a viable option for the design of high-performance deep-blue TADF materials.

High-Contrast Visualization Chemiluminescence Based on AIE-Active and Base-Sensitive Emitters.

Peroxyoxalate chemiluminescence (PO-CL) is one of the most popular cold light sources, yet the drawback of aggregation-caused quenching limits their use. Here, we report a new kind of efficient bifunctional emitter derived from salicylic acid, which not only exhibits typical aggregation-induced emission (AIE) character but also has the ability to catalyze the CL process under basic conditions based on base sensitivity. By taking advantage of these unique features, we successfully confine the CL process on the surface of solid bases and provide a high-contrast visualization of CL emission. This method allows most of the common basic salts like sodium carbonate to be invisible encryption information ink and PO-CL solution to be a decryption tool to visualize the hidden information. The current study opens up an appealing way for the development of multifunction CL emitters for information encryption and decryption applications.

Efficient Spin-Flip between Charge-Transfer States for High-Performance Electroluminescence, without an Intermediate Locally Excited State.

Thermally activated delayed fluorescence (TADF) materials with both high photoluminescence quantum yield (PLQY) and fast reverse intersystem crossing (RISC) are strongly desired to realize efficient and stable organic light-emitting diodes (OLEDs). Control of excited-state dynamics via molecular design plays a central role in optimizing the PLQY and RISC rate of TADF materials but remains challenging. Here, 3 TADF emitters possessing similar molecular structures, similar high PLQYs (89.5% to 96.3%), and approximate energy levels of the lowest excited singlet states (S1), but significantly different spin-flipping RISC rates (0.03 × 106 s-1 vs. 2.26 × 106 s-1) and exciton lifetime (297.1 to 332.8 µs vs. 6.0 µs) were systematically synthesized to deeply investigate the feasibility of spin-flip between charge-transfer excited states (3CT-1CT) transition. Experimental and theoretical studies reveal that the small singlet-triplet energy gap together with low RISC reorganization energy between the 3CT and 1CT states could provide an efficient RISC through fast spin-flip 3CT-1CT transition, without the participation of an intermediate locally excited state, which has previously been recognized as being necessary for realizing fast RISC. Finally, the OLED based on the champion TADF emitter achieves a maximum external quantum efficiency of 27.1%, a tiny efficiency roll-off of 4.1% at 1,000 cd/m2, and a high luminance of 28,150 cd/m2, which are markedly superior to those of the OLEDs employing the other 2 TADF emitters.

Optoelectronic performance of perovskite Cs2KMI6 (M = Ga, In) based on high-throughput screening and first-principles calculations.

Developing novel lead-free perovskite materials with suitable bandgaps and superior thermal stability is crucial to boost their applications in next-generation photovoltaic technologies. High throughput screening combined with the first principles method can accurately and effectively screen out promising perovskites. Herein, we select two lead-free all-inorganic halide double perovskite materials Cs2KMI6 (M = Ga, In) from 1026 compounds with the criteria including appropriate structure factors, positive decomposition energies, and suitable direct bandgaps. We investigated the thermal and mechanical stability, geometric and electronic structures, photoelectric properties, and defect formation energies for both perovskites Cs2KMI6 (M = Ga, In). They can exhibit excellent structural formability and stability through the analysis of structure factors, elastic constants, and stable chemical potential regions. In addition, we investigate the defect effects of Cs2KMI6 (M = Ga, In) on the photovoltaic performance by evaluating the defect formation energies and transition energy levels. Based on the HSE06 functional, we calculated the energy band structures of these two compounds and demonstrate the direct bandgaps of 1.69 eV (HSE06) and 2.16 eV (HSE06) for Cs2KGaI6 and Cs2KInI6, respectively. Moreover, we predicted excellent spectroscopic limited maximum efficiencies (SLMEs) of these two perovskites with high light absorption coefficients (around 105 cm-1), for instance, the SLME of Cs2KGaI6 can reach as high as 28.39%.

Cerium Synchronous Doping in Anatase for Enhanced Photocatalytic Hydrogen Production from Ethanol-Water Mixtures.

Cerium element with a unique electric structure can be used to modify semiconductor photocatalysts to enhance their photocatalytic performances. In this work, Ce-doped TiO2 (Ce/TiO2) was successfully achieved using the sol-gel method. The structural characterization methods confirm that Ce was doped in the lattice of anatase TiO2, which led to a smaller grain size. The performance test results show that the Ce doped in anatase TiO2 significantly enhances the charge transport efficiency and broadens the light absorption range, resulting in higher photocatalytic performance. The Ce/TiO2 exhibited a photocurrent density of 10.9 µA/cm2 at 1.0 V vs. Ag/AgCl, 2.5 times higher than that of pure TiO2 (4.3 µA/cm2) under AM 1.5 G light. The hydrogen (H2) production rate of the Ce/TiO2 was approximately 0.33 µmol/h/g, which is more than twice as much as that of the pure anatase TiO2 (0.12 µmol/h/g). This work demonstrates the effect of Ce doping in the lattice of TiO2 for enhanced photocatalytic hydrogen production.

Cerium-Doped Iron Oxide Nanorod Arrays for Photoelectrochemical Water Splitting.

In this work, a simple one-step hydrothermal method was employed to prepare the Ce-doped Fe2O3 ordered nanorod arrays (CFT). The Ce doping successfully narrowed the band gap of Fe2O3, which improved the visible light absorption performance. In addition, with the help of Ce doping, the recombination of electron/hole pairs was significantly inhibited. The external voltage will make the performance of the Ce-doped sample better. Therefore, the Ce-doped Fe2O3 has reached superior photoelectrochemical (PEC) performance with a high photocurrent density of 1.47 mA/cm2 at 1.6 V vs. RHE (Reversible Hydrogen Electrode), which is 7.3 times higher than that of pristine Fe2O3 nanorod arrays (FT). The Hydrogen (H2) production from PEC water splitting of Fe2O3 was highly improved by Ce doping to achieve an evolution rate of 21 µmol/cm2/h.

Correction: Efficiently increasing the radiative rate of TADF material with metal coordination.

Correction for 'Efficiently increasing the radiative rate of TADF material with metal coordination' by Xian-Bao Cai et al., Chem. Commun., 2022, 58, 8970-8973, https://doi.org/10.1039/D2CC02930H.

Pollen Carbon-Based Rare-Earth Composite Material for Highly Efficient Photocatalytic Hydrogen Production from Ethanol-Water Mixtures.

The unique electronic structure of rare-earth elements makes their modified semiconductor photocatalysts show great advantages in solar energy conversion. Herein, the pollen-like N, P self-doped biochar-based rare-earth composite catalyst (Er/LP-C) has been successfully synthesized, which combines the advantages of biochar and Er and is used for the first time in the field of photocatalytic hydrogen production from ethanol-water mixtures. Experimental results confirmed that the performance of photocatalytic hydrogen production under the full spectrum is up to 33.70 µmol/g in 6 h; this is due to the introduction of Er, which improves the carrier concentration, separation and transfer efficiency, and the driving force for the reduction reaction.

Voltage-Dependent Emission Varying from Blue to Orange-Red from a Nondoped Organic Light-Emitting Diode with a Single Emitter.

Organic light-emitting diodes (OLEDs) with tunable emission colors, especially white OLEDs, have rarely been observed with a single emitter in a single emissive layer. In this paper, we report a new compound featuring a D-A-D structure, 9,9'-(pyrimidine-2,5-diylbis(2,1-phenylene))bis(3,6-di-tert-butyl-9H-carbazole) (PDPC). A nondoped OLED using this compound as a single emitter exhibits unique voltage-dependent dual emission. The emission colors range from blue to orange-red with an increase in voltage, during which white electroluminescence with a Commission Internationale De L'Eclairage (CIE) coordinate of (0.35, 0.29) and a color render index (CRI) value of 93 was observed. A comparative study revealed that the dual emission simultaneously originates from the monomers and excimers of the emitter. This study provides insight into understanding the multimer-excited mechanism and developing novel color-tunable OLEDs.

Efficiently increasing the radiative rate of TADF material with metal coordination.

Herein, a simple and straightforward method to reduce dramatically the lifetime of a pure organic thermally activated delayed fluorescence (TADF) material VIA metal coordination is demonstrated. We designed a mononuclear silver complex [Ag(PPh2CH3)(TCzBN-PyPz)]BF4 (1) with a new emissive TCzBN-PyPz ligand. Even though the ligand and the metal complex have very similar emissive efficiencies and maximal peaks, over three orders of magnitude shorter lifetime of 0.59 µs for the complex than 2074 µs for ligand were obtained. Compared to other methods, the present protocol seems to be simple and highly effective.

N, P Self-Doped Porous Carbon Material Derived from Lotus Pollen for Highly Efficient Ethanol-Water Mixtures Photocatalytic Hydrogen Production.

Porous biochar materials prepared with biomass as a precursor have received widespread attention. In this work, lotus pollen (LP) was used as the carbon source, a variety of the pollen carbon photocatalyst were prepared by a two-step roasting method. A series of characterizations were carried out on the prepared samples, and it was found that the average particle size was about 40 µm. They also exhibit a typical amorphous carbon structure and a porous structure with a network-like interconnected surface. The photocatalytic hydrogen production performances of lotus pollen carbon (LP-C) and commercial carbon black (CB) were measured under the full spectrum illumination. LP-C-600 showed the best hydrogen production performance (3.5 µmol·g-1·h-1). In addition, the photoelectrochemical (PEC) measurement results confirmed that the LP-C materials show better incident photon-current efficiency (IPCE) performance than the CB materials in the neutral electrolyte. This is because the unique surface wrinkling, hierarchical porous structure, and the N, P self-doping behavior of the LP-C samples are able to improve the light utilization efficiency and the carrier separation/transfer efficiency, thereby further improving the overall hydrogen production efficiency.

Thermally activated delayed fluorescence materials with aggregation-induced emission properties: a QM/MM study.

Organic molecules with thermally activated delayed fluorescence (TADF) and aggregation induced emission (AIE) properties have attracted increasing research interest due to their great potential applications in organic light emitting diodes (OLEDs), especially for those with multicolor mechanochromic luminescence (MCL) features. Theoretical research on the luminescence characteristics of organic TADF emitters based on the aggregation states is highly desired to quantify the relationship between the TADF properties and aggregation states. In this work, we study the 4,4'-(6-(9,9-dimethylacridine-10(9H)-yl)quinoline-2,3-dibenzonitrile (DMAC-CNQ) emitter with TADF and AIE properties, and calculate the photophysical properties in gas, solid and amorphous states by using the quantum mechanics and molecular mechanics (QM/MM) method. Our simulations demonstrate that the aggregation states enhance obviously the reverse intersystem crossing rates and transition dipole moments of the DMAC-CNQ emitter, and suppress the non-radiative rates from the lowest excited singlet state (S1) to ground state (S0). Specifically, the molecular stacking of DMAC-CNQ in solid phases can mainly restrict the geometric torsion of the DMAC moiety for decreasing non-radiative decay rates, and the torsion of the CNQ moiety for increasing the reverse intersystem crossing rates. As a result, the calculated fluorescence efficiencies of the DMAC-CNQ emitter in the crystal and amorphous states are 67% and 26% respectively, and in good agreement with the experimental results.

Thermally Activated Delayed Fluorescence Amorphous Molecular Materials for High-Performance Organic Light-Emitting Diodes.

Small-molecule thermally activated delayed fluorescence (TADF) materials have been extensively developed to actualize efficient organic LEDs (OLEDs). However, organic small molecules generally compromise thin film quality and stability due to the tendency of crystallization, aggregation, and phase separation, which hence degrade the efficiency and long-term stability of the OLEDs. Here, for the first time, we exploit the unique molecular configuration of the bimesitylene scaffold to design two highly efficient TADF amorphous molecular materials with excellent thermal and morphological stabilities. The twisted and rigid bimesitylene scaffold thwarts regular molecular packing and crystallization, thereby guaranteeing homogeneous and stable amorphous thin films. Meanwhile, the highly twisted geometry of the bimesitylene scaffold efficiently breaks the molecular conjugation and thus conserves the high energies of the lowest locally excited triplet states (3LE) above the lowest charge transfer states (1CT and 3CT), leading to small singlet-triplet energy splitting and fast reverse intersystem crossing. These TADF emitters exhibit high photoluminescence quantum yields of 0.90 and 0.69 and short TADF lifetimes of 4.94 and 1.44 µs in doped films, based on which the greenish-blue and greenish-yellow OLEDs achieve external quantum efficiencies of 23.2 and 16.2%, respectively, with small efficiency roll-off rates and perfect color stability.