Highly efficient perovskite QLEDs can be realized when QD films possess two crucial synergistic parameters: highly luminescent features and effective electric transport properties. Regarding the emissive properties of QD films, although long organic ligands perfectly passivated the QD's surface and endowed ink with the near-unity luminescent properties with a PLQY approaching 100%, [11,12] the films generally exhibited a relatively low PLQY of about 40% due to the formation of nonradiative recombination centers. This phenomenon results from the dynamic characteristic of the bonding between the QD's surface and organic capping ligands, leading to the mismatched ligands during the film-forming process. [13,14] Meanwhile, these ligands act as electrically insulating layers on the QD's surface resulting in inefficient carrier injection and transportation, [15,16] which are detrimental to device performance. To enhance the electric properties of QD films, much attention [17,18] has been devoted to the development of ligand strategies that minimize the interparticle spacing. For example, Li et al. demonstrated an effective enhancement in electrical properties and EQE of CsPbBr 3 QLEDs through the control of surface ligand density. [9] Through ligand-exchange strategies, [8,19] a relatively short (C12) ligand, didodecyl dimethyl ammonium bromide (DDAB), was used to enhance device performance, obtaining an EQE of 8.73% under an effective washing process. Unfortunately, these methods are still based on long organic ligands, which cannot render the QD solid with ideal carrier injection and transportation features. Thus, it is significantly crucial to find an effective and feasible strategy to control the surface state of perovskite QDs, which could guarantee the high exciton recombination and carrier injection in constructing high-performance electroluminescent (EL) devices.Inorganic ligands with less space separation among particles could effectively enhance the electrical properties of QD films. [20,21] Meanwhile, they also improved the PL features through the reduce of the defect-related nonradiative recombination, which has been proven in traditional QDs. [22][23][24][25] For example, the halide-related ligands have improved the luminescent feature and radiative recombination in Cd-based QDs, which was realized by the ligand-exchange process. [20,26,27] But such a strategy is not feasible for perovskite QDs because they Perovskite quantum dots (QDs) with high photoluminescence quantum yields (PLQYs) and narrow emission peak hold promise for next-generation flexible and high-definition displays. However, perovskite QD films often suffer from low PLQYs due to the dynamic characteristics between the QD's surface and organic ligands and inefficient electrical transportation resulting from long hydrocarbon organic ligands as highly insulating barrier, which impair the ensuing device performance. Here, a general organic-inorganic hybrid ligand (OIHL) strategy is reported on to passivate perovskite QDs for highly efficient el...

An efficient fragment-based approach for predicting the ground-state energies and structures of large molecules at the Hartree-Fock (HF) and post-HF levels is described. The physical foundation of this approach is attributed to the "quantum locality" of the electron correlation energy and the HF total energy, which is revealed by a new energy decomposition analysis of the HF total energy proposed in this work. This approach is based on the molecular fractionation with conjugated caps (MFCC) scheme (Zhang, D. W.; Zhang, J. Z. H. J. Chem. Phys. 2003, 119, 3599), by which a macromolecule is partitioned into various capped fragments and conjugated caps formed by two adjacent caps. We find that the MFCC scheme, if corrected by the interaction between non-neighboring fragments, can be used to predict the total energy of large molecules only from energy calculations on a series of small subsystems. The approach, named as energy-corrected MFCC (EC-MFCC), computationally achieves linear scaling with the molecular size. Our test calculations on a broad range of medium- and large molecules demonstrate that this approach is able to reproduce the conventional HF and second-order Moller-Plesset perturbation theory (MP2) energies within a few millihartree in most cases. With the EC-MFCC optimization algorithm described in this work, we have obtained the optimized structures of long oligomers of trans-polyacetylene and BN nanotubes with up to about 400 atoms, which are beyond the reach of traditional computational methods. In addition, the EC-MFCC approach is also applied to estimate the heats of formation for a series of organic compounds. This approach provides an appealing approach alternative to the traditional additivity rules based on either bond or group contributions for the estimation of thermochemical properties.

The epigenetic regulation of imprinted genes via monoallelic DNA methylation of either maternal or paternal alleles is critical for embryonic growth and development1. Imprinted genes were recently shown to be expressed in mammalian adult stem cells to support self-renewal of neural and lung stem cells2, 3,4; however, a role for imprinting per se in adult stem cells remains elusive. Here we show up-regulation of growth-restricting imprinted genes, including within the H19-Igf2 locus5, in long-term hematopoietic stem cells (LT-HSCs) and their down-regulation upon HSC activation and proliferation. A differentially methylated region (DMR) upstream of H19 (H19-DMR), serving as the imprinting control region, determines the reciprocal expression of H19 from the maternal allele and Igf2 from the paternal allele1. In addition, H19 also serves as a source of miR-675, which restricts Igf1r expression6. We demonstrated that conditional deletion of the maternal but not the paternal H19-DMR reduced adult HSC quiescence, a state required for long-term maintenance of HSCs, and compromised HSC function. Maternal-specific H19-DMR deletion resulted in activation of the Igf2-Igfr1 pathway as revealed by the translocation of phosphorylated Foxo3 (an inactive form) from nucleus to cytoplasm and the release of Foxo3-mediated cell-cycle arrest, thus leading to increased activation, proliferation, and eventual exhaustion of HSCs. Mechanistically, maternal-specific H19-DMR deletion led to Igf2 up-regulation and increased translation of Igf1r, which is normally suppressed by H19-derived miR-675. Similarly, genetic inactivation of Igf1r partially rescued the H19-DMR deletion phenotype. Our work establishes a novel role for this unique form of epigenetic control at the H19-Igf2 locus in maintaining adult stem cells.

Perovskite quantum-dot-based light-emitting diodes (QLEDs) possess the features of wide gamut and real color expression, which have been considered as candidates for high-quality lightings and displays. However, massive defects are prone to be reproduced during the quantum dot (QD) film assembly, which would sorely affect carrier injection, transportation and recombination, and finally degrade QLED performances. Here, we propose a bilateral passivation strategy through passivating both top and bottom interfaces of QD film with organic molecules, which has drastically enhanced the efficiency and stability of perovskite QLEDs. Various molecules were applied, and comparison experiments were conducted to verify the necessity of passivation on both interfaces. Eventually, the passivated device achieves a maximum external quantum efficiency (EQE) of 18.7% and current efficiency of 75 cd A −1. Moreover, the operational lifetime of QLEDs is enhanced by 20-fold, reaching 15.8 h. These findings highlight the importance of interface passivation for efficient and stable QD-based optoelectronic devices.