Fabrication of red-emitting perovskite LEDs by stabilizing their octahedral structure.

Light-emitting diodes (LEDs) based on metal halide perovskites (PeLEDs) with high colour quality and facile solution processing are promising candidates for full-colour and high-definition displays1-4. Despite the great success achieved in green PeLEDs with lead bromide perovskites5, it is still challenging to realize pure-red (620-650 nm) LEDs using iodine-based counterparts, as they are constrained by the low intrinsic bandgap6. Here we report efficient and colour-stable PeLEDs across the entire pure-red region, with a peak external quantum efficiency reaching 28.7% at 638 nm, enabled by incorporating a double-end anchored ligand molecule into pure-iodine perovskites. We demonstrate that a key function of the organic intercalating cation is to stabilize the lead iodine octahedron through coordination with exposed lead ions and enhanced hydrogen bonding with iodine. The molecule synergistically facilitates spectral modulation, promotes charge transfer between perovskite quantum wells and reduces iodine migration under electrical bias. We realize continuously tunable emission wavelengths for iodine-based perovskite films with suppressed energy loss due to the decrease in bond energy of lead iodine in ionic perovskites as the bandgap increases. Importantly, the resultant devices show outstanding spectral stability and a half-lifetime of more than 7,600 min at an initial luminance of 100 cd m-2.

Tautomeric mixture coordination enables efficient lead-free perovskite LEDs.

Lead halide perovskite light-emitting diodes (PeLEDs) have demonstrated remarkable optoelectronic performance1-3. However, there are potential toxicity issues with lead4,5 and removing lead from the best-performing PeLEDs-without compromising their high external quantum efficiencies-remains a challenge. Here we report a tautomeric-mixture-coordination-induced electron localization strategy to stabilize the lead-free tin perovskite TEA2SnI4 (TEAI is 2-thiopheneethylammonium iodide) by incorporating cyanuric acid. We demonstrate that a crucial function of the coordination is to amplify the electronic effects, even for those Sn atoms that aren't strongly bonded with cyanuric acid owing to the formation of hydrogen-bonded tautomeric dimer and trimer superstructures on the perovskite surface. This electron localization weakens adverse effects from Anderson localization and improves ordering in the crystal structure of TEA2SnI4. These factors result in a two-orders-of-magnitude reduction in the non-radiative recombination capture coefficient and an approximately twofold enhancement in the exciton binding energy. Our lead-free PeLED has an external quantum efficiency of up to 20.29%, representing a performance comparable to that of state-of-the-art lead-containing PeLEDs6-12. We anticipate that these findings will provide insights into the stabilization of Sn(II) perovskites and further the development of lead-free perovskite applications.

Correction: Atomically flat semiconductor nanoplatelets for light-emitting applications.

Correction for 'Atomically flat semiconductor nanoplatelets for light-emitting applications' by Bing Bai et al., Chem. Soc. Rev., 2023, 52, 318-360, https://doi.org/10.1039/D2CS00130F.

Atomically flat semiconductor nanoplatelets for light-emitting applications.

The last decade has witnessed extensive breakthroughs and significant progress in atomically flat two-dimensional (2D) semiconductor nanoplatelets (NPLs) in terms of synthesis, growth mechanisms, optical and electronic properties and practical applications. Such NPLs have electronic structures similar to those of quantum wells in which excitons are predominantly confined along the vertical direction, while electrons are free to move in the lateral directions, resulting in unique optical properties, such as extremely narrow emission line width, short photoluminescence (PL) lifetime, high gain coefficient, and giant oscillator strength transition (GOST). These unique optical properties make NPLs favorable for high color purity light-emitting applications, in particular in light-emitting diodes (LEDs), backlights for liquid crystal displays (LCDs) and lasers. This review article first introduces the intrinsic characteristics of 2D semiconductor NPLs with atomic flatness. Subsequently, the approaches and mechanisms for the controlled synthesis of atomically flat NPLs are summarized followed by an insight on recent progress in the mediation of core/shell, core/crown and core/crown@shell structures by selective epitaxial growth of passivation layers on different planes of NPLs. Moreover, an overview of the unique optical properties and the associated light-emitting applications is elaborated. Despite great progress in this research field, there are some issues relating to heavy metal elements such as Cd2+ in NPLs, and the ambiguous gain mechanisms of NPLs and others are the main obstacles that prevent NPLs from widespread applications. Therefore, a perspective is included at the end of this review article, in which the current challenges in this stimulating research field are discussed and possible solutions to tackle these challenges are proposed.

Universal Molecular Control Strategy for Scalable Fabrication of Perovskite Light-Emitting Diodes.

Despite the rapid progress in perovskite light-emitting diodes (PeLEDs), the electroluminescence performance of large-area perovskite devices lags far behind that of laboratory-size ones. Here, we report a 3.5 cm × 3.5 cm large-area PeLED with a record-high external quantum efficiency of 12.1% by creating an amphipathic molecular interface modifier of betaine citrate (BC) between the perovskite layer and the underlying hole transport layer (HTL). It is found that the surface wettability for various HTLs can be efficiently improved as a result of the coexistence of methyl and carboxyl groups in the BC molecules that makes favorable groups to selectively contact with the HTL surface and increases the surface free energy, which greatly facilitates the scalable process of solution-processed perovskite films. Moreover, the luminous performance of perovskite emitters is simultaneously enhanced through the coordination between C═O in the carboxyl groups and Pb dangling bonds.

Ciclopirox olamine sensitizes leukemia cells to natural killer cell-mediated cytolysis by upregulating NKG2DLs via the Akt signaling pathway.

The activating receptor natural killer group 2D (NKG2D) expressed by Natural killer (NK) cells functions as a "master-switch" in governing the awakening status of NK cells. The NKG2D-mediated cytotoxicity has been declared to be related with the expression levels of NKG2D ligands (NKG2DLs) expressed on tumor cells. Therefore, selective induction of NKG2DLs could be a reliable approach to enhance the efficacy of NK cell-mediated immunotherapy. Our existing study demonstrated that Ciclopirox Olamine (CPX), an off-patent antifungal agent, effectively elevated the expression of NKG2DLs on leukemia cells and sensitized leukemia cells to NK-cell mediated cytolysis. Induction of ROS production and AKT phosphorylation by CPX is essential for the up-regulation of NKG2DLs expressions. Inhibition of AKT by using AKT inhibitor MK2206 decreased both NKG2DLs expressions and NK cell cytotoxicity. These data indicated that increased sensitivity of CPX-treated leukemia cells to NK cell cytolysis was attributed to higher NKG2DLs expressions, resulting from activated AKT signaling pathway. Our findings support the ongoing development of CPX as an anti-tumor agent and suggest its promising immunotherapeutic value in the medication of leukemia.

Core/Shell ZnO/ZnS Nanoparticle Electron Transport Layers Enable Efficient All-Solution-Processed Perovskite Light-Emitting Diodes.

Solution-processed perovskite-based light-emitting diodes (PeLEDs) are promising candidates for low-cost, large-area displays, while severe deterioration of the perovskite light-emitting layer occurs during deposition of electron transport layers from solution in an issue. Herein, core/shell ZnO/ZnS nanoparticles as a solution-processed electron transport layer in PeLED based on quasi-2D PEA2 Csn-1 Pbn Br3n+1 (PEA = phenylethylammonium) perovskite are employed. The deposition of ZnS shell mitigates trap states on ZnO core by anchoring sulfur to oxygen vacancies, and at the same time removes residual hydroxyl groups, which helps to suppress the interfacial trap-assisted non-radiative recombination and the deprotonation reaction between the perovskite layer and ZnO. The core/shell ZnO/ZnS nanoparticles show comparably high electron mobility to pristine ZnO nanoparticles, combined with the reduced energy barrier between the electron transport layer and the perovskite layer, improving the charge injection balance in PeLEDs. As a result, the optimized PeLEDs employing core/shell ZnO/ZnS nanoparticles as a solution-processed electron transport layer exhibit high peak luminance reaching 32 400 cd m-2 , external quantum efficiency of 10.3%, and 20-fold extended longevity as compared to the devices utilizing ZnO nanoparticles, which represents one of the highest overall performances for solution-processed PeLEDs.

Mixed-Dimensional MXene-Based Composite Electrodes Enable Mechanically Stable and Efficient Flexible Perovskite Light-Emitting Diodes.

Significant advancements in perovskite light-emitting diodes (PeLEDs) based on ITO glass substrates have been realized in recent years, yet the overall performance of flexible devices still lags far behind, mainly being ascribed to the high surface roughness and poor optoelectronic properties of flexible electrodes. Here, we report efficient and robust flexible PeLEDs based on a mixed-dimensional (0D-1D-2D-3D) composite electrode consisting of 0D Ag nanoparticles (AgNPs)/1D Ag nanowires (AgNWs)/2D MXene/3D poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). Our designed MXene-based electrodes combine the advantages of facile formation of a film of low-dimensional materials and excellent optical and electrical properties of metal, inorganic, and organic semiconductors, which endow the electrodes with high electrical/thermal conductivity, flexibility, a smooth surface, and good transmittance. Consequently, the resulting flexible PeLEDs (without a light-coupling structure) demonstrate a record external quantum efficiency of 16.5%, a high luminance of close to 50000 cd/m2, a large emitting area of 8 cm2, and significantly enhanced mechanical stability.

A Multifunctional Ionic Liquid Additive Enabling Stable and Efficient Perovskite Light-Emitting Diodes.

The electroluminescence performance and long-term stability of perovskite light-emitting diodes (PeLEDs) are greatly affected by the film quality of perovskite emitting layer. Herein, the authors employ an ionic liquid, 1-butyl-3-methylimidazolium trifluoromethanesulfonate ([BMIm]OTf), to manipulate the growth of quasi-2D perovskite films by providing heterogeneous nucleation sites. The [BMIm]OTf molecules simultaneously realize uniform perovskite films by reducing the contact angles of precursor solution on the hole transport layer (HTL), and eliminate defect states through bonding [BMIm]+ cations to negatively-charged uncoordinated Br and OTf- anions to uncoordinated Pb2+ defects that effectively suppresses the defect states assisted nonradiative recombination in perovskite films. As a result, the efficiency and the operational lifetime of the resultant PeLED are enhanced by more than twofold and threefold, respectively, achieving a maximum external quantum efficiency of 17.6% and an operational lifetime of over 500 min at an initial brightness of 100 cd m-2 .

Deep-Blue Electroluminescence of Perovskites with Reduced Dimensionality Achieved by Manipulating Adsorption-Energy Differences.

The lagging development of deep-blue perovskite light-emitting diodes (PeLEDs) heavily impedes their practical applications in full-color display due to the absence of spectrally stable emitters and the mismatch of carrier injection capacity. Herein, we report highly efficient deep-blue PeLEDs through a new chemical strategy that addresses the dilemma for simultaneously constant electroluminescence (EL) spectra and high-purify phase in reduced-dimensional perovskites. The success lies in the control of adsorption-energy differences between phenylbutylamine (PBA) and ethylamine (EA) interacting with perovskites, which facilitates narrow n-value distribution. This approach leads to an increased exciton binding energy and enhanced surface potential, hence improving radiative recombination. As a result, an external quantum efficiency of 4.62 % is achieved in PeLEDs with a stable EL peak at 457 nm, demonstrating the best reported result for deep-blue PeLEDs so far.

Parthenolide inhibits ubiquitin-specific peptidase 7 (USP7), Wnt signaling, and colorectal cancer cell growth.

It has been well-established that the deubiquitinating enzyme ubiquitin-specific peptidase 7 (USP7) supports cancer growth by up-regulating multiple cellular pathways, including Wnt/ß-catenin signaling. Therefore, considerable efforts are directed at identifying and developing USP7 inhibitors. Here, we report that sesquiterpene lactone parthenolide (PTL) inhibits USP7 activity, assessed with deubiquitinating enzyme activity assays, including fluorogenic Ub-AMC/Ub-Rho110, Ub-VME/PA labeling, and Di-Ub hydrolysis assays. Further investigations using cellular thermal shift (CETSA), surface plasmon resonance (SPR), and mass spectrum (MS) assays revealed that PTL directly interacts with USP7. Consistent with the role of USP7 in stimulating Wnt signaling and carcinogenesis, PTL treatment inhibited the activity of Wnt signaling partly by destabilizing ß-catenin. Moreover, using cell viability assays, we found that PTL suppresses the proliferation of colorectal cancer cells and induces apoptosis in these cells. Additionally, we examined the effects of two other sesquiterpene lactones (costunolide and α-santonin) on USP7 and Wnt signaling and found that α-methylene-γ-butyrolactone may provide a scaffold for future USP7 inhibitors. In summary, our findings reveal that PTL inhibits USP7 activity, identifying a potential mechanism by which PTL suppresses Wnt/ß-catenin signaling. We further suggest that sesquiterpene lactones might represent a suitable scaffold for developing USP7 inhibitors and indicate that PTL holds promise as an anticancer agent targeting aberrant USP7/Wnt signaling.

USP47 maintains the stemness of colorectal cancer cells and is inhibited by parthenolide.

Colorectal cancer stem cells (CCSCs) are implicated in colorectal tumor initiation, invasion, recurrence and treatment resistance, so elucidation of the mechanism underlying the cancer stem cells induction and development of drugs targeting CCSCs are vital for cancer treatment. Growing evidence shows that dysregulated deubiquitinase (DUBs) expression is frequently associated with stemness and maintenance of cancer stem cells (CSCs). In the current study, we found that upregulation of USP47 is associated with tumorigenesis and poor prognosis in clinical patients with colorectal cancer (CRC). Besides, USP47 was highly expressed in CCSCs enriched by serum-free culture. Further investigation showed that USP47 is closely involved in the maintenance of the stemness of CCSCs. USP47 silencing reduces proliferation and migration of colorectal cancer cells and suppresses the self-renewal of CCSCs by downregulating the expression of cancer stem cell markers, including CD44, CD133, CD166, OCT4 and NANOG. Furthermore, we identified Parthenolide (PTL), a natural sesquiterpene lactone, as a novel USP47 inhibitor. PTL diminishes CCSCs self-renewal and induces apoptosis of CCSCs. Taken together, our findings highlighted a novel DUB involved in the modulation of CCSCs stemness and the potential of PTL in the CRC treatment by targeting CCSCs as the USP47 inhibitor.

All-Inorganic Quantum Dot Light-Emitting Diodes with Suppressed Luminance Quenching Enabled by Chloride Passivated Tungsten Phosphate Hole Transport Layers.

Although excellent performance such as high efficiency and stability have been achieved in quantum dot (QD)-based light-emitting diodes (QLEDs) possessing an organic/inorganic hybrid device structure, the highly expected all-inorganic QLEDs remain at the bottleneck stage in recent years, resulting from the luminance quenching of QDs caused by inorganic hole transport layer (HTL) and unbalanced charge injection due to large energy barrier for injecting holes from HTL to QDs. Here, it is reported that the solution-processed inorganic environmentally friendly chloride (Cl)-passivated tungsten phosphate (Cl@TPA) films serve as HTL. The incorporation of Cl in TPA effectively passivates the oxygen vacancies, which not only avoids the luminescence quenching of QDs by reducing carrier concentration but also facilitates the hole injection from HTL to QDs with a favorable electronic band alignment, thus achieving the record external quantum efficiency of ≈9.27%, among all previous reports about all-inorganic QLEDs. Most importantly, the resulting all-inorganic QLEDs with Cl@TPA exhibit a substantial improvement in the operational lifetime (T50  > 105 h under an initial luminance of 100 cd m-2 ), which is almost 30-fold higher than the devices with TPA HTL. This work furnishes a promising strategy for highly efficient and stable QLEDs based on inorganic device structure.

Antimicrobial Peptide Brevinin-1RL1 from Frog Skin Secretion Induces Apoptosis and Necrosis of Tumor Cells.

Cancer has always been one of the most common malignant diseases in the world. Therefore, there is an urgent need to find potent agents with selective antitumor activity against cancer cells. It has been reported that antimicrobial peptides (AMPs) can selectively target tumor cells. In this study, we focused on the anti-tumor activity and mechanism of Brevinin-1RL1, a cationic α-helical AMP isolated from frog Rana limnocharis skin secretions. We found that Brevinin-1RL1 preferentially inhibits tumor cells rather than non-tumor cells with slight hemolytic activity. Cell viability assay demonstrated the intermolecular disulfide bridge contributes to the inhibitory activity of the peptide as the antitumor activity was abolished when the disulfide bridge reduced. Further mechanism studies revealed that both necrosis and apoptosis are involved in Brevinin-1RL1 mediated tumor cells death. Moreover, Brevinin-1RL1 induced extrinsic and mitochondria intrinsic apoptosis is caspases dependent, as the pan-caspase inhibitor z-VAD-FMK rescued Brevinin-1RL1 induced tumor cell proliferative inhibition. Immunohistology staining showed Brevinin-1RL1 mainly aggregated on the surface of the tumor cells. These results together suggested that Brevinin-1RL1 preferentially converges on the cancer cells to trigger necrosis and caspase-dependent apoptosis and Brevinin-1RL1 could be considered as a pharmacological candidate for further development as anti-cancer agent.

Discovery of isopenicin A, a meroterpenoid as a novel inhibitor of tubulin polymerization.

Microtubules are involved in celluar processes of movement, intracellular trafficking and mitosis, thus microtubule-targeting agents have been widely used in cancer therapy. Herein, we report isopenicin A, a novel meroterpenoid isolated from the plant endophytic fungus of Penicillium sp. sh18, as a novel microtubule binding molecule that efficiently depolymerizes microtubule polymerization to evoke G2/M cell cycle arrest and subsequent cell apoptosis, contributing to proliferation inhibition of human tumor cell lines. The discovery of isopenicin A provides a new chemotype for discovery and development of promising microtubule inhibitors.

Molecule-Induced p-Doping in Perovskite Nanocrystals Enables Efficient Color-Saturated Red Light-Emitting Diodes.

Color-saturated red light-emitting diodes (LEDs) with emission wavelengths at around 620-640 nm are an essential part of high-definition displays. Metal halide perovskites with very narrow emission linewidth are promising emitters, and rapid progress has been made in perovskite-based LEDs (PeLEDs); however, the efficiency of the current color-pure red PeLEDs-still far lags behind those of other-colored ones. Here, a simple but efficient strategy is reported to gradually down-shift the Fermi level of perovskite nanocrystals (NCs) by controlling the interaction between NCs and their surface molecular electron acceptor-benzyl iodide with aromatic rings-and realize p-doping in the color-saturated 625 nm emitting NCs, which significantly reduces the hole injection barrier in devices. Besides, both the luminescence efficiency and electric conductivity of perovskite NCs are enhanced as additional advantages as the result of surface defects passivation. As a result, the external quantum efficiency for the resulting LED is increased from 4.5% to 12.9% after benzyl iodide treatment, making this device the best-performing color-saturated red PeLED so far. It is further found that the hole injection plays a more critical role than the photoluminescence efficiency of perovskite emitter in determining the LED performance, which implies design principles for efficient thin-film planar LEDs.

Physalis peruviana-Derived 4ß-Hydroxywithanolide E, a Novel Antagonist of Wnt Signaling, Inhibits Colorectal Cancer In Vitro and In Vivo.

Deregulation of the Wnt signaling pathway leads to colorectal cancer progression. Natural dietary compounds serve as promising candidates for development as chemopreventive agents by suppressing the Wnt/ß-catenin signaling pathway. Physalis peruviana-derived 4ßHWE showed a significant inhibitory activity with a calculated IC50 of 0.09 µΜ in a screening of novel inhibitors of Wnt signaling with the dual-luciferase reporter assay. This study investigated the anti-tumor effect of 4ßHWE and the potential Wnt signaling inhibitory mechanism. Both the western blot analysis and immunofluorescence assay showed that 4ßHWE promoted the phosphorylation and degradation of ß-catenin and the subsequent inhibition of its nuclear translocation to attenuate the endogenous Wnt target gene expression in colorectal cancer (CRC) cells. The cell viability assay indicated that 4ßHWE preferentially inhibited the proliferation of CRC compared with CCD-841-CoN, a normal human colonic epithelial cell line. 4ßHWE-mediated G0/G1 cell cycle arrest and apoptosis induction contributed to the suppression of the proliferation of CRC in the cell cycle and Annexin V-FITC/Propidium Iodide apoptosis analysis. Moreover, in vivo, 4ßHWE dramatically inhibited tumor growth in HCT116 xenografts by attenuating the Wnt/ß-catenin signaling pathway. In conclusion, our study suggested that 4ßHWE could be of potential use in anti-tumor agent development as a novel Wnt signaling inhibitor.

Aurovertin B sensitizes colorectal cancer cells to NK cell recognition and lysis.

The natural killer group 2D (NKG2D) receptor on natural killer (NK) cells play an important role in immunosurveillance to cancer cells, which could mediate the eradication of tumor cells through specific interactions with NKG2D ligands on tumor cells. Here we report one natural compound aurovertin B from basidiomycete Albatrellus confluens significantly stimulates the expression of NKG2D ligands on tumor cells, which greatly sensitizes its recognition and lysis by NK cell. It is completely a novel role for aurovertin B to target tumor cells to death mediated by NK cells and our findings indicate aurovertin B may deserve further development as sensitizing agent in NK cell mediated cancer immunotherapy.

Enantioselective N-Heterocyclic Carbene-Catalyzed Synthesis of Spirocyclic Oxindole-benzofuroazepinones.

Herein, we report an enantioselective synthesis of azepinones via the N-heterocyclic carbene (NHC) catalyzed [3+4] annulation reaction of isatin-derived enals and aurone-derived azadienes. The corresponding spirocyclic oxindole-benzofuroazepinones were obtained in good yields, with excellent diastereo- and enantioselectivities. The resulted azepinones were evaluated for their in vitro cytotoxic activities against six human tumor cell lines, with two compounds showing significant inhibitory activity comparable with that of cisplatin.