Shi-Zheng Wen

Theoretical exploration to second-order nonlinear optical properties of new hybrid complexes via coordination interaction between (metallo)porphyrin and [MSiW11O39]3− (M = NbV or VV) polyoxometalates

The second-order nonlinear optical (NLO) properties of hybrid complexes via coordination interaction between porphyrin and Keggin-type polyoxometalates (POMs) α-[MSiW11O39](3-) (M=Nb(V) or V(V)) are investigated by time-dependent density functional theory (TDDFT). The calculated results show that this kind of organic-inorganic hybrid complexes possesses remarkably large molecular second-order NLO polarizability, especially for the ZnP3P-C≡C-4-Py-[VSiW11O39](3-) (complex 4), which has a computed β0 value of 261,410 a.u. and might be an excellent second-order NLO material. The effects of substituted metal atom (M), metalloporphyrin, and π-conjugation on NLO response are analyzed, the substituted metal atom (M) with a large electronegativity, the metalloporphyrin, and the lengthening of π-conjugation are helpful in enhancing the optical nonlinearity of these systems, which reveal the general rules to design the complexes with large optical nonlinearities. Furthermore, the solvent effect largely affects the first-order hyperpolarizability of the complex, it implies that the second-order polarizabilities increased with the increase of the solvent in polarity.

Theoretical insights into [PMo12O40](3-) grafted on single-walled carbon nanotubes.

Nano-hybrid materials based on a combination of polyoxometalate (POM) clusters and single-walled carbon nanotubes (SWNT) exhibit a great interesting application in molecular cluster batteries. The interactions between POM and SWNT and their detailed electronic properties have been investigated by employing first-principles calculations. Various models were constructed to study the geometries, interactions (binding sites and energies), and charge transfer behavior. Analysis of charge distributions reveals two different charge transfer characteristic depending on the type of POM interaction with SWNT. The simulation provides insight into the optimal structures in lieu of interfacial stability. Finally, the implications of these results for understanding the properties of molecular cluster batteries are discussed.

Time-Dependent Current Distributions of a Two-Terminal Carbon Nanotube-Based Electronic Device

We have performed time-dependent density-functional theory calculations to simulate the transient electrical response of a carbon nanotube-based electronic device. Time-dependent current density and electrostatic potential distribution are calculated and analyzed. Strong local vortices are observed for the current. In addition, the calculated dynamic admittance confirms that the dynamic response of the two-terminal device can be mapped onto the equivalent electric circuit reported in our previous work [Yam et al. Nanotechnology 2008, 19, 495203].

Theoretical study on the rectifying performance of organoimido derivatives of hexamolybdates.

We design a new type of molecular diode, based on the organoimido derivatives of hexamolybdates, by exploring the rectifying performances using density functional theory combined with the non-equilibrium Greens function. Asymmetric current-voltage characteristics were obtained for the models with an unexpected large rectification ratio. The rectifying behavior can be understood by the asymmetrical shift of the transmission peak observed under different polarities. It is interesting to find that the preferred electron-transport direction in our studied system is different from that of the organic D-bridge-A system. The results show that the studied organic-inorganic hybrid systems have an intrinsically robust rectifying ratio, which should be taken into consideration in the design of the molecular diodes.

TDDFT studies on chiral organophosphonate substituted divacant Keggin-type polyoxotungstate: diplex multistep-redox-triggered chiroptical and NLO switch

We theoretically investigate a novel switching phenomenon based on the divacant Keggin-type polyoxotungstate bearing chiral organophosphonate [{NH(2)CH(CH(3))PO}(2)(γ-SiW(10)O(36))](4-), that is the synchronous chiroptical and nonlinear optical (NLO) switch triggered by redox. The ECD calculations on the Boltzmann weighted conformations of the three oxidation states of this chiral polyoxometalate (POM) clearly present a chiroptical switching process. The electronic transition and the bond-length alternation studies show that the chirality transfer from chiral carbon atom to POM cage increases as the polyanion is reduced. Simultaneously, the static first hyperpolarizability of studied chiral POM quadrupled from the oxidized state to the 1e-reduced state, and is further doubled to the 2e-reduced state, which is mainly due to the increasing electronic-dipole-allowed d-d charge transfer transitions in the POM cage. This work firstly reproduces the ECD spectrum of chiral POM with high accuracy and proves the possibility for confirming the molecular conformations of flexible chiral POMs in solution by the aid of ECD calculations. Most importantly, a sensitive diplex switch based on a chiral POM is predicted in theory, which may aid the design of novel POM-based switches.

Cd(II) and Cu(II) coordination polymers based on a multidentate N-donor ligand: syntheses, crystal structures, optical band gaps, and photoluminescence

Four Cd(II)- and Cu(II)-containing coordination polymers (CPs) based on a multidentate N-donor ligand and varied dicarboxylate anions, [Cd(3,3′-tmbpt)(p-bdc)]·2.5H2O (1), [Cd(3,3′-tmbpt)(m-bdc)]·2H2O (2), [Cu(3,3′-tmbpt)(m-bdc)]·H2O (3), and [Cu(3,3′-tmbpt)(p-bdc)]·2H2O (4), where 3,3′-tmbpt = 1 − ((1H-1,2,4-triazol-1-yl)methyl)-3,5-bis(3-pyridyl)-1,2,4-triazole, p-H2bdc = 1,4-benzenedicarboxylic acid, and m-H2bdc = 1,3-benzenedicarboxylic acid, have been prepared hydrothermally. The structures of the compounds were determined by single-crystal X-ray diffraction analyses and further characterized by infrared spectra and elemental analyses. Compound 1 exhibits a 3-D twofold interpenetrating framework with a 65·8 CdSO4 topology. Compound 2 is a 2-D layer containing meso-helical chains with a 44·62 sql topology. Compound 3 shows a 1-D → 3-D interdigitated architecture while 4 displays a 2-D → 3-D interdigitated architecture. The structural differences of the compounds indicate that the dicarboxylate anions and the central metal ions play important roles in the resulting structures of CPs. Optical band gaps and solid-state photoluminescent properties have also been studied. Graphical abstract

Syntheses, structures, and photocatalysis of five inorganic–organic hybrid compounds constructed from Keggin polyoxometalate clusters and multidentate N-donor ligands

Five inorganic–organic hybrid compounds have been prepared under hydrothermal conditions and characterized by single-crystal X-ray diffraction analyses, infrared spectra, elemental analyses, powder X-ray diffraction, and thermogravimetric analyses. In 1, each 2,2ʹ-tmbpt ligand links two Cu(II) ions to generate a highly undulated chain. The chains are further bridged by [SiW12O40]4‒ anions to form a layer. Compound 2 exhibits a 3-D (3,4,5)-connected framework with large channels, in which [SiW12O40]4‒ anions are tetradentate linkages. In 3, each 2,4ʹ-tmbpt links three Cu(II) ions to form 2-D layers, which are further linked by [SiW12O40]4‒ to yield a 3-D (3,4)-connected framework. In 4, each 4,4ʹ-tmbpt connects three Cu(II) ions to generate 1-D double chains. In 5, [PW12O40]3‒ link Cu(II) ions to generate 1-D chains. Compounds 1‒5 exhibit photocatalytic activities for degradation of methylene blue and rhodamine B. Graphical Abstract Five inorganic–organic hybrid compounds have been synthesized, and the photocatalytic properties of the compounds have also been studied.

First principle investigation of transport properties of Lindqvist derivatives based molecular junction

The transport properties of Lindqvist type-polyoxometalates H₂Mo₆O₁₉ (M=Mo, W) sandwiched between carbon nanotube electrodes are investigated by using density functional theory combined with the non-equilibrium Greens function method. It is found that the precise position of the protonation has little effect on the transport properties of H₂Mo₆O₁₉, as it is established by investigating two different geometries. Furthermore we have discovered that H₂Mo₆O₁₉ and H₂Mo₆O₁₉ display similar conduction profiles with the main conduction mechanism being quantum tunneling. With a large energy gap and robust structural stability these molecules appear to be good candidate for high bias applications.

Theoretical investigation of armchair silicene nanoribbons with application in stretchable electronics

The electronic and transport properties of a series of 11-ASiNRs (armchair silicene nanoribbons) at different torsion angles were studied by using density functional theory combined with nonequilibrium Greens function method. Several key factors determining the transport properties, such as the electron transmission coefficient and band structure, have been discussed. The interesting results suggest that the transport properties of ASiNRs are insensitive to the torsional silicene nanoribbon configuration in the scattering region. With the increase of the torsion angle, the transmission coefficient is still well maintained within the limits of the torsion angle. Although the torsion angle is increased to 120°, the current dropped by just 22% compared to the initial 11-ASiNRs at a torsion angle of 0°. Furthermore, all the configurations of 11-ASiNRs in this study behave as conventional conductors with nearly linear current–voltage dependence. On the basis of these distinctive transport properties with metabolic structure, ASiNRs present potential promising applications in silicon-based electronic nanodevices.

Theoretical investigation of second-order nonlinear optical response by linking hexamolybdate with graphene in the donor–acceptor (D–A) framework

The graphenes and polyoxometalates (POMs) have been investigated individually for finding a material with intrinsic nonlinear optical (NLO) behaviours. In this study, we designed a novel molecular hybrid containing POM cluster linked with nanographene. We could be able to design a material with very large second-order NLO response. The Coulomb-attenuating method (CAM–B3LYP) is used with the LANL2DZ basis set for molybdenum atoms and both 6–31G (d) and 6–31+G (d) basis sets for main group elements to calculate polarisability and first hyperpolarisability. The second-order polarisability of the system is significantly enhanced by replacing NH2 or NO2 with hexamolybdate in [NO2–HBC(derivative of hexabenzocoronene)–NH2] from 33.33 × 10− 30 esu (system 1) to 57.71 × 10− 30 esu (system 2) and 231.10 × 10− 30 esu (system 3), respectively. The time-dependent density functional theory (TDDFT) calculations show that the charge transfer from polyanion to graphene in systems 2 and 3 is responsible for the NLO properties of this kind of compound. We believe that the novel designed link between graphene and POMs is a door for further studies to find materials with an excellent NLO response.