Yongqin Wei

Magnetic properties of nonmetal atoms absorbed MoS2 monolayers

The geometries, electronic structures, and magnetic properties of H-, B-, C-, N-, O-, and F-absorbed MoS2 monolayers have been investigated by first-principles calculations. The results demonstrate that all these atoms can chemically absorb on MoS2 monolayer. The total magnetic moments of H-, B-, C-, N-, and F-absorbed MoS2 monolayers are 1.0, 1.0, 2.0, 1.0, and 1.0 μB, respectively. The large spatial extensions of spin density and long-range antiferromagnetic coupling were observed in H- and F-absorbed MoS2 monolayers. Additionally, the n-type and p-type two-dimensional MoS2 semiconductors can be realized by absorbing H and N atoms, respectively.

A white-light-emitting LnMOF with color properties improved via Eu3+ doping: an alternative approach to a rational design for solid-state lighting

The intrinsic white-light-emitting properties of a lanthanide metal-organic framework that approach requirements for solid-state lighting are easily improved by incorporating minute quantities of red-emitting Eu(3+) into the host framework by virtue of the isostructural character of the La(3+) and Eu(3+) compounds and efficient sensitization of ligands toward Eu(3+) ions.

Two cobalt(II) coordination polymers [Co2(H2O)4(Hbidc)2]n and [Co(Hbidc)]n (Hbidc = 1H-benzimidazole-5,6-dicarboxylate): syntheses, crystal structures, and magnetic properties

Two novel cobalt(II) coordination polymers [Co2(H2O)4(Hbidc)2]n (1) and [Co(Hbidc)]n (2), (Hbidc = 1H-benzimidazole-5,6-dicarboxylate) were synthesized hydrothermally by treating CoSO4 and H3bidc at 160 or 220 °C, respectively. X-Ray diffraction analyses showed that compound 1 is a 1-D chain polymer with dimer units [Co2(H2O)4(Hbidc)2] and the infinite chains of compound 1 array uniformly towards the crystallographic a-axis in a 3-D supramolecular framework which possesses abundant hydrogen-bonding interactions between uncoordinated carboxylo-oxygen atoms and coordinated water molecules or N–H groups in imidazole rings. Compound 2 is a novel five-coordinated cobalt(II) chain compound exhibiting a 2-D polymeric network with parallel zip-like cobalt–carboxylate chains along the crystallographic b-axis and the 2-D polymeric networks of compound 2 exhibit a layered arrangement, in which the strong hydrogen-bonding interaction between uncoordinated carboxylo-oxygen atoms and N–H groups in the imidazole rings play a key role in the final 3-D supramolecular architectures. Magnetic studies revealed that compound 1 shows a ferromagnetic coupling between two CoII ions in the dimer unit and compound 2 exhibits an antiferromagnetic property.

A chirally helical coordination polymer self-assembled with the ligand 2-(2-carboxyphenyl)imidazo(4,5-f)(1,10)phenanthroline: crystal structure, SHG response and tunable photoluminescence

A chirally helical coordination polymer [Zn(H2O)(ONCP)Cl]n self-assembled with ligand 2-(2-carboxyphenyl)imidazo(4,5-f)(1,10)phenanthroline displays second harmonic generation efficiency, which is approximately two times as much as that of potassium dihydrogen phosphate (KDP), and tunable photoluminescence images form yellow-green to white based on the variation of excitation light.

Direct metal-metal interaction contributions to quadratic hyperpolarizability: A study on dirhenium complexes

We present a comparative study of the metal-metal interaction effect on the static quadratic hyperpolarizabilities of two typical dinuclear rhenium clusters. The electronic structures, excitation spectra, dipolar moments, static polarizabilities, and quadratic hyperpolarizabilities of the two complexes with direct metal-metal interactions have been computed and analyzed with the use of high-level DFT/TDDFT methods. The geometries and the first intense excitations agree with the relevant reported measurements. The orbital decomposition scheme ( J. Phys. Chem. A 2006, 110, 1014-1021) has been applied to analyze the relationship between the electronic structures and nonlinear optical (NLO) properties of these two complexes. We propose an unprecedented NLO response mechanism featuring the contribution of the direct metal-metal interaction transition process in these dinuclear rhenium complexes. This contribution positively enhances the quadratic hyperpolarizability and relates to the intensity of the metal-metal interactions of the complexes. The results are helpful to the development of NLO chromophores in polynuclear metal clusters through the molecular design technique.

Explosive boiling of a metallic glass superheated by nanosecond pulse laser ablation

We report an explosive boiling in a Zr-based (Vitreloy 1) bulk metallic glass irradiated by a nanosecond pulse laser with a single shot. This critical phenomenon is accompanied by the ejection of high-temperature matter from the target and the formation of a liquid-gas spinodal pattern on the irradiated area. An analytical model reveals that the glassy target experiences the normal heating (melting) and significant superheating, eventually culminating in explosive boiling near the spinodal limit. Furthermore, the time lag of nucleation and the critical radius of vapor bubbles are theoretically predicted, which are in agreement with the experimental observations. This study provides the investigation on the instability of a metallic glass liquid near the thermodynamic critical temperature.

Spontaneous resolution of a homochiral helix built from a tetra-nuclear nickel cluster

A chirally helical coordination polymer [Ni4(H2O)7L4·H2O]n (H2222L = 2-(pyridin-2-yl)-1H-imidazole-4,5-dicarboxylic acid) constructed from a Ni4L4 building block exhibits spontaneous chiral resolution and the enantiomers of 1M and 1P have been confirmed by single-crystal analysis and solid-state circular dichroism spectra. The magnetic properties of compound 1 are also discussed.

A highly stable and white-light-emitting Eu(III) MOF

A long π-conjugated organic ligand 2-(2,4-disulfophenyl)imidazo(4,5-f)(1,10)-phenanthroline (H3sfpip) featuring blue-green emission was used to construct Eu(iii) MOFs to obtain a target white-light-emitting LnMOF with no dopant atom in its structure. Two complexes, [Eu(H2O)2(OH)(Hsfpip)]·H2O (1) and [Eu(H2O)(oa)0.5(Hsfpip)]·2H2O (2), were successfully synthesized under similar hydrothermal reaction conditions. The absence or presence of an ancillary ligand such as oxalic acid (oa) showed direct influence on the coordination mode of the Hsfpip linker and in the final topology of the polymeric structure. Complex 1 displays an unstable 2D polymeric structure and weak red luminescence from Eu3+ due to the quenching effect of high-energy O-H oscillators around the inner coordination sphere of the metal center, whereas the introduction of an ancillary ligand such as oxalic acid results in a tight-bonding 3D polymeric structure and an intense white light emission from complex 2. Moreover, due to the skeleton rigidity and robustness of complex 2, the white light emission can be improved via a heating process.

Novel Acentric Organic Solids with Non-linear Optical and Ferroelectric Properties

A series of compounds obtained through one-pot three-component reaction, present non-centrosymmetric polar packing arrangement, resulting in strong second harmonic generation responses and ferroelectric behaviours.

Modulating the electronic structures and optical absorption spectra of BeO nanotubes by uniaxial strain

The electronic structures, optical absorption spectra, and the modulation of uniaxial strain along tube axis to electronic structures and optical absorption spectra of BeO nanotubes have been studied using the density functional theory. The results show that the absorption spectrum of BeO nanotubes is anisotropic with respect to light polarization and is closely related to the chirality and diameter of tube. The uniaxial strain can effectively modulate the electronic structures and absorption spectra of BeO nanotubes, indicating the armchair BeO nanotubes can be used as the anisotropic device and sensor of photoelectron.