lichenliu1991

Bis-β-ketoimine ligands of the form [(CH₂)_n{N(H)C(Me)CHC(Me)O}₂] (LⁿH₂, n=2, 3 and 4) were employed in the formation of a range of gallium complexes [Ga(Lⁿ)X] (X=Cl, Me, H), which were characterised by NMR spectroscopy, mass spectrometry and single-crystal X-ray diffraction analysis. The β-ketoimine ligands have also been used for the stabilisation of rare gallium hydride species [Ga(Lⁿ)H] (n=2 (7); n=3 (8)), which have been structurally characterised for the first time, confirming the formation of five-coordinate, monomeric species. The stability of these hydrides has been probed through thermal analysis, revealing stability at temperatures in excess of 200 °C. The efficacy of all the gallium β-ketoiminate complexes as molecular precursors for the deposition of gallium oxide thin films by chemical vapour deposition (CVD) has been investigated through thermogravimetric analysis and deposition studies, with the best results being found for a bimetallic gallium methyl complex [L³{GaMe₂}₂] (5) and the hydride [Ga(L³)H] (8). The resulting films (F5 and F8, respectively) were amorphous as-deposited and thus were characterised primarily by XPS, EDXA and SEM techniques, which showed the formation of stoichiometric (F5) and oxygen-deficient (F8) Ga₂O₃ thin films.

Making vapor: Thermally stable gallium hydrides are formed by utilizing tetradentate β-ketoimine ligand systems (see scheme). The monomeric species are isolated and structurally characterized, and their application as molecular precursors to gallium oxide thin films is also shown. The study highlights the potential of this ligand class for the facile preparation of traditionally unstable species, rendering them suitable for further application in materials fabrication.

Two new solution-processable wide bandgap materials, bis(4-((4-(9-H-carbazol-9-yl)phenyl)diphenylsilyl)phenyl)(phenyl)phosphine oxide (CS₂PO) and bis(4-((4-(9-H-(3,9′-bicarbazol)-9-yl)phenyl)diphenylsilyl)phenyl)(phenyl)phosphine oxide (DCS₂PO), have been developed for blue phosphorescent light-emitting diodes by coupling an electron-donating carbazole moiety and an electron-accepting PO unit together via double-silicon bridges. Both of them have been characterized as having high glass transition temperatures of 159–199 °C, good solubility in common organic solvent (20 mg mL⁻¹), wide optical gap (3.37–3.55 eV) and high triplet energy levels (2.97–3.04 eV). As compared with their corresponding single-silicon bridged compounds, this design strategy of extending molecular structure endows CS₂PO and DCS₂PO with higher thermal stability, better solution processability and more stable film morphology without lowering their triplet energies. As a result, DCS₂PO/FIrpic doped blue phosphorescent device fabricated by spin-coating method shows the best electroluminescent performance with a maximum current efficiency of 26.5 cd A⁻¹, a maximum power efficiency of 8.66 lm W⁻¹, and a maximum external quantum efficiency of 13.6%, which is one of the highest efficiencies among small molecular devices with the same deposition process and device configuration.

Solution-processable wide-bandgap materials are synthesized by incorporating carbazole and PO moieties into double-bridged tetraphenylsilanes. This design strategy endows them with good solubility, high thermal stability, and excellent film-forming ability without lowering the triplet energies. A maximum current efficiency of 26.5 cd A⁻¹ and external quantum efficiency of 13.6% is achieved for DCS₂PO/FIrpic blue phosphorescent device.

A facile method is presented for the large-scale preparation of rationally designed mesocrystalline MnO@carbon core–shell nanowires with a jointed appearance. The nanostructures have a unique arrangement of internally encapsulated highly oriented and interconnected MnO nanorods and graphitized carbon layers forming an external coating. Based on a comparison and analysis of the crystal structures of MnOOH, Mn₂O₃, and MnO@C, we propose a sequential topotactic transformation of the corresponding precursors to the products. Very interestingly, the individual mesoporous single-crystalline MnO nanorods are strongly interconnected and maintain the same crystallographic orientation, which is a typical feature of mesocrystals. When tested for their applicability to Li-ion batteries (LIB), the MnO@carbon core–shell nanowires showed excellent capacity retention, superior cycling performance, and high rate capability. Specifically, the MnO@carbon core–shell nanostructures could deliver reversible capacities as high as 801 mA h g⁻¹ at a high current density of 500 mA g⁻¹, with excellent electrochemical stability after testing over 200 cycles, indicating their potential application in LIBs. The remarkable electrochemical performance can mainly be attributed to the highly uniform carbon layer around the MnO nanowires, which is not only effective in buffering the structural strain and volume variations of anodes during repeated electrochemical reactions, but also greatly enhances the conductivity of the electrode material. Our results confirm the feasibility of using these rationally designed composite materials for practical applications. The present strategy is simple but very effective, and appears to be sufficiently versatile to be extended to other high-capacity electrode materials with large volume variations and low electrical conductivities.

MnO-based nanowires: MnO@C core–shell composite nanostructures with a jointed appearance can be prepared via Mn₂O₃ (see scheme). The nanostructures consist of internally encapsulated MnO and carbon layers forming an exterior coating. These MnO@C core–shell nanowires show relatively good capacity retention, thus making them promising materials for application in lithium-ion batteries.