Cesium lead halide (CsPbX) nanocrystals have emerged as a new family of materials that can outperform the existing semiconductor nanocrystals due to their superb optical and charge-transport properties. However, the lack of a robust method for producing quantum dots with controlled size and high ensemble uniformity has been one of the major obstacles in exploring the useful properties of excitons in zero-dimensional nanostructures of CsPbX. Here, we report a new synthesis approach that enables the precise control of the size based on the equilibrium rather than kinetics, producing CsPbX quantum dots nearly free of heterogeneous broadening in their exciton luminescence. The high level of size control and ensemble uniformity achieved here will open the door to harnessing the benefits of excitons in CsPbX quantum dots for photonic and energy-harvesting applications.

Blue host materials for organic light-emitting diodes (OLEDs) based on silicon-cored (tetraphenylsilane) anthracene derivatives are synthesized. These compounds, with a non-coplanar molecular structure, have high glass-transition temperatures and good amorphous-film-forming capabilities. When doped with a blue-fluorescent dopant, blue emission with high color purity and high efficiency, up to 7.5 cd A(-1) and 6.3%, is achieved.

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Liquid crystalline polyethers have been synthesized from 1-(4-hydroxy-4‘-biphenylyl)-2-(4-hydroxyphenyl)propane and α,ω-dibromoalkanes with even-numbers of methylene units [TPP(n = even)s]. Multiple phase transitions are found during cooling and heating via differential scanning calorimetry (DSC), and they show little undercooling dependence. Ordered structure identifications are based on experimental observations of wide angle X-ray powder and fiber diffraction experiments at different temperatures. Polarized light and transmission electron microscopy observations on mesophase morphology combined with DSC results on thermodynamic transition properties also provide additional evidence for these phase assignments. Moreover, the contributions of the mesogenic groups and the methylene units to each ordering process are obtained based on the changes of transition enthalpy and entropy. In TPP(n ≤ 8)s the highest temperature transition is from the isotropic melt to a nematic phase. This nematic phase is only stable in a narrow temperature range. For instance, it is 12 °C for TPP(n = 4) and 6 °C for TPP(n = 8). When the number of methylene units n ≥ 10, the isotropic melt directly enters a smectic F phase. The second transition in TPP(n ≤ 8)s is from the nematic to the smectic F phase. As a result, the smectic F phase exists for all TPP(n = even)s. Decreasing the temperature further leads to another transition in TPP(n = even)s to form a smectic crystal G phase which is followed by a transition to a smectic crystal H phase. This smectic crystal H phase remains for TPP(n ≤ 8)s down to their glass transition temperatures, while in TPP(n ≥ 10)s further ordering processes occur and crystal phases are observed. A phase diagram of TPP(n = even)s is constructed.

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Lithium–sulfur (Li–S) batteries by far offer higher theoretical energy density than that of the commercial lithium-ion battery counterparts, but suffer predominantly from an irreversible shuttling process involving lithium polysulfides. Here, we report a fluorinated covalent organic polymer (F-COP) as a template for high performance sulfur cathodes in Li–S batteries. The fluorination allowed facile covalent attachment of sulfur to a porous polymer framework via nucleophilic aromatic substitution reaction (SNAr), leading to high sulfur content, e.g., over 70 wt %. The F-COP framework was microporous with 72% of pores within three well-defined pore sizes, viz. 0.58, 1.19, and 1.68 nm, which effectively suppressed polysulfide dissolution via steric and electrostatic hindrance. As a result of the structural features of the F-COP, the resulting sulfur electrode exhibited high electrochemical performance of 1287.7 mAh g–1 at 0.05C, 96.4% initial Columbic efficiency, 70.3% capacity retention after 1000 cycles at 0.5C, and robust operation for a sulfur loading of up to 4.1 mgsulfur cm–2. Our findings suggest the F-COP family with the adaptability of SNAr chemistry and well-defined microporous structures as useful frameworks for highly sustainable sulfur electrodes in Li–S batteries.

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In-plane strains are commonly found in two-dimensional (2D) metal halide organic–inorganic perovskites (HOIPs). The in-plane mechanical properties of 2D HOIPs are vital for mitigating the strain-induced stability issues of 2D HOIPs, yet their structure and mechanical property relationship largely remains unknown. Here, we employed atomic force microscope indentation to systematically investigate the in-plane Young’s moduli E ∥ of 2D lead halide Ruddlesden–Popper HOIPs with a general formula of (R-NH3)2PbX4, where the spacer molecules R-NH3 + are linear alkylammonium cations (C m H2m+1-NH3 +, m = 4, 6, 8, or 12) and X = I, Br, or Cl. Fixing the spacer molecule to butylammonium, we discovered that the E ∥ of 2D HOIPs generally follows the trend of Pb–X bond strength, different from the tendency found in the out-of-plane moduli E ⊥, showing more prominent effects of the metal halide inorganic framework on E ∥ than E ⊥. E ∥ exhibits nonmonotonic dependence on the chain length of the linear alkyl spacer molecules, which would first decrease and plateau but then increase again. This is likely due to the competition of the bond strength and structural distortion in the inorganic layer, the relative fraction of the soft organic spacers, and the interfacial mechanical coupling associated with the interdigitation of the alkyl chains. The mechanical anisotropy of 2D HOIPs, marked by E ∥/E ⊥, shows wide tunability based on structural composition, particularly for iodide-based 2D HOIPs. Our results provide valuable insights into the structure–property relationships regarding the mechanical anisotropy and in-plane mechanical behaviors of 2D HOIPs, which can guide the materials design and device optimization to achieve required mechanical performance in 2D HOIP-based applications.