Kechen Wu

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.

Cadmium-rare earth oxyborates Cd4ReO(BO3)3 (Re = Y, Gd, Lu): congruently melting compounds with large SHG responses

A new series of cadmium–rare earth (Re) oxyborates Cd4ReO(BO3)3 (Re = Y, Gd, Lu) have been synthesized through high-temperature solid-state reactions in platinum crucibles. In their crystal structures, ReO6 (Re = Y, Gd, Lu) and CdOn (n = 6, 8) are distorted polyhedra interconnected via shared edges and corners in a 3D framework with tunnels along the c-axis, where all B atoms are located. BO3 planar triangles lie approximately parallel to the (001) plane. The combination of triangular BO3 groups with π-conjugated systems and the d10 Cd2+ cation with polar displacement produces large SHG responses. Second harmonic generation (SHG) measurements indicate that Cd4YO(BO3)3, Cd4GdO(BO3)3, and Cd4LuO(BO3)3 feature large SHG responses that are approximately 5.2, 5.0, and 5.3 × KH2PO4 (KDP), respectively. They are all phase matchable nonlinear optical materials that have wide transparent regions ranging from UV to near IR. These title compounds melt congruently, suggesting that the Cd4ReO(BO3)3 (Re = Y, Gd, Lu) complexes are very promising NLO materials. Their electronic structures and optical properties were analyzed by using the Vienna ab initio theoretical method.

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.

A new hybrid DFT approach to electronic excitation and first hyperpolarizabilities of transition metal complexes.

The electronic excitations and the static first hyperpolarizability of three typical transition metal (TM) aromatic carbonyl complexes, two tungsten pentacarbonyl derivatives (W(CO)5L, L = Py and PyCHO) and one chromium tricarbonyl arene derivative (Cr(CO)3Bz, Bz = benzene), have been theoretically studied by a variety of density functional methods. The assessments reveal that most of the conventional DFT methods including local density approximation, generalized gradient approximation (GGA), and the various kinds of hybrid exchange‐correlation (xc) methods present the first hyperpolarizabilities of these TM‐containing molecules with large deviations from the experiments. A one‐parameter hybrid xc functional is introduced by using the Perdew‐Wang 1991 gradient‐corrected correlation functional (PW91) and the Barones‐modified PW91 exchange functional (mPW). The ratio between the exact and the density functional exchange is determined to be 0.40 by the adiabatic connection method. The application of the new hybrid functional to the three organometallic carbonyl molecules results in the satisfactory agreement between the calculated first hyperpolarizabilities and the experimental ones. The second‐order nonlinear optical properties of the three organometallic complexes are addressed to the metal‐to‐ligand charge transfers, and the extended π‐delocalization ligands benefit the enhancement of the first hyperpolarizability.

Anisotropic thermoelectric properties of layered compounds in SnX2 (X = S, Se): a promising thermoelectric material

Thermoelectrics interconvert heat to electricity and are of great interest in waste heat recovery, solid-state cooling and so on. Here we assessed the potential of SnS2 and SnSe2 as thermoelectric materials at the temperature gradient from 300 to 800 K. Reflecting the crystal structure, the transport coefficients are highly anisotropic between a and c directions, in particular for the electrical conductivity. The preferred direction for both materials is the a direction in TE application. Most strikingly, when 800 K is reached, SnS2 can show a peak power factor (PF) of 15.50 μW cm(-1) K(-2) along the a direction, while a relatively low value (11.72 μW cm(-1) K(-2)) is obtained in the same direction of SnSe2. These values are comparable to those observed in thermoelectrics such as SnSe and SnS. At 300 K, the minimum lattice thermal conductivity (κmin) along the a direction is estimated to be about 0.67 and 0.55 W m(-1) K(-1) for SnS2 and SnSe2, respectively, even lower than the measured lattice thermal conductivity of Bi2Te3 (1.28 W m(-1) K(-1) at 300 K). The reasonable PF and κmin suggest that both SnS2 and SnSe2 are potential thermoelectric materials. Indeed, the estimated peak ZT can approach 0.88 for SnSe2 and a higher value of 0.96 for SnS2 along the a direction at a carrier concentration of 1.94 × 10(19) (SnSe2) vs. 2.87 × 10(19) cm(-3) (SnS2). The best ZT values in SnX2 (X = S, Se) are comparable to that in Bi2Te3 (0.8), a typical thermoelectric material. We hope that this theoretical investigation will provide useful information for further experimental and theoretical studies on optimizing the thermoelectric properties of SnX2 materials.

Theoretical studies on the nonlinear optical susceptibilities of 3-methoxy-4-hydroxy-benzaldehyde crystal

Abstract Nonlinear optical susceptibilities of a SHG material, 3-methoxy-4-hydroxy-benzaldehyde (MHBA), were investigated at both molecular and crystalline levels, by using the MP2 (second-order level of Moller–Plesset perturbation correction) method and the oriented-gas approximation. The results revealed that the electron donor group –OH and acceptor group –HCO play important roles in the magnitude of second-order polarizabilities. The studies of the oriented-gas model showed the crystal has large nonlinear optical coefficients, d 22 =23.8 d 36 KDP , d 21 =13.5 d 36 KDP , d 23 =29.1 d 36 KDP , d 25 =12.8 d 36 KDP , which agree well with the experimental results.

Nonlinear optical properties of some derivatives of stilbene and vinyl cyanide

Three derivatives of stilbene: 3-hydroxy-4-methoxy-4′-nitrostilbene (HMONS), 3-methoxy-4-hydroxy-4′-nitro-stilbene (MOHNS), 2-cyano-3-indole-propenoic acid ethyl ester (CIP-ethyl), and one derivative of vinyl cyanide: p-1,1-dicyano-vinyl-dimethylaminoaniline (DVDA) were designed and synthesized. The powder second-harmonic generation and absorption spectra of these four compounds were measured. First principle calculation of the molecular first hyperpolarizabilities of HMONS were calculated and compared with those of 3-methyl-4-methoxy-4′-nitrostilbene (MMONS, Appl. Phys. Lett. 56 (1990) 423) in order to elucidate their structural origin of the optical nonlinearity.

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.