Chensheng Lin

Density functional theory studies on the potential energy surface and hyperpolarizability of polyamidoamide dendrimer

Abstract The potential energy surface and hyperpolarizabilities of the core (G0) and the first generation (G1) of polyamidoamide (PAMAM) dendrimer are studied by using the density functional theory with both the basis sets optimized for B3LYP method and the medium-size polarized GTO/CGTO basis sets for calculations of molecular polarizability. The inversion barrier of G1 is 941.4 cm −1 , which indicates that the back folding of the branches is very easy for this dendrimer construction. It is found that in most cases, the first hyperpolarizabilities β of G1 will increased when the molecular structure is distorted from its equilibrium arrangement. These results provide structural guidelines for the optimization of β by means of changing the dendrimer shape in different solvents.

Synthesis, structure and possible formation pathway of a novel cobalt carbonyl compound with new type BO bond, Co(CO)3(PPh3)2BEt3, and mixed metal CoFeS cluster with possible nonlinear optical property, [Et4N][CoFe2(CO)8S(PPh3)]

Reaction of Co(CNS) 2 with Fe 2 S 2 (CO) 6 , LiBEt 3 H and PPh 3 in THFue5f8MeCN resulting in a novel cobalt carbonyl complex, Co(CO) 3 (PPh 3 ) 2 BEt 3 ( 1 ) and mixed-metal Coue5f8Feue5f8S cluster compound, [Et 4 N][Fe 2 Co(CO) 8 S(PPh 3 )] ( 2 ). The structures of 1 and 2 were determined from X-ray three dimension data. Structure studies reveal that 1 is a new cobalt carbonyl complex containing a novel Bue5f8O bond of 1.601(5) A in which the oxygen atom is from metal carbonyl and the B atom is from BEt 3 and 2 contained a triangular pyramid mixed-metal Coue5f8Feue5f8S core [CoFe 2 S] − with Coue5f8S of 2.189, Feue5f8S of 2.208, Coue5f8Fe of 2.56 and Feue5f8Fe of 2.58 A. Theoretical calculation on 1 and 2 shows that Bue5f8O bonding energy of complex 1 is lower than that of normal covalent bonding and 2 possesses a calculated nonlinear optical first molecular hyperpolarizability component of 28.5×10 −30 esu. The possible formation pathway of 1 and 2 was discussed.

Theoretical studies of nonlinear optical crystals in metal cluster compounds

Theoretical studies and simulations have been applied to explore novel nonlinear optical crystals in metal clusters. The structure-nonlinear optical property relationships of a series of metal cluster molecules have been investigated theoretically within the density functional theory framework. For example, the polarizability and hyperpolarizability of a set of three-nuclear metal cluster compounds of the Mo(W)/Cu(Ag, An) sulfur system are calculated to elucidate the influence of the geometric configuration and the element substitution effect; a set of potential second harmonic generation (SHG) metal cluster crystals are studied and simulated such as the MoAg(2)S5(Py)(PPh3)(2), MoS4Cu4I2(Py)(6) clusters. The results indicate that many of these crystals are promising SHG crystals that may be applied in the infrared (IR) spectroscopic region. The studies are useful to aid in screening, simulating and designing novel nonlinear optical crystals in metal cluster compounds, especially those to be applied in medium/far-IR region

Large hyperpolarizabilities of trinuclear transition metal clusters [MAg2X4(C5H5NS)(PPh3)2]·CH2Cl2 (M = Mo, W; X = S, Se): a DFT study

Static and dynamic first hyperpolarizabilities have been studied by a DFT approach for a series of trinuclear heterometallic transition metal molecular clusters, [MAg2X4(C5H5NS)(PPh3)2]·CH2Cl2 (M = Mo, W; X = S, Se) with incomplete cubane-like configurations. Their nonlinear optical nature has been analyzed by using a two-level model. The large hyperpolarizabilities of about 100 × 10−30 esu of these metal clusters are generated by intermolecular charge transfers from the metal core to the pyridine-2-thiol ligand as well as by intramolecular charge transfers within the metal core. The conjoint effects of stereo π (3D) conjugation of the metal core and planar π (2D) conjugation of the C5H5NS ligand enhance these hyperpolarizabilities, while the presence of CH2Cl2 has a negative effect by lowering them. Since these complexes are all crystallized in noncentrosymmetric configurations, they are promising candidates as IR second-order nonlinear optical transition metal coordinated materials.

Mixed metal pentanuclear clusters [MFe4S4(CO)12]z− (M=V, Mn and Cr; z=0, 2) and X-ray crystal structures of [VFe4S4(CO)12] and [MnFe4S4(CO)12]2−

Abstract Reaction of VCL 3 , MnCl 2 and CrCl 3 +Zn with [Fe 2 S 2 (CO) 6 ] 2− , from reduction of [Fe 2 S 2 (CO) 6 ] by LiEt 3 BH, resulting in pentanuclear mixed metal clusters [VFe 4 S 4 (CO) 12 ] ( 1 ), [Et 4 N] 2 [MnFe 4 S 4 (CO) 12 ] ( 2 ) and [Et 4 N] 2 [CrFe 4 S 4 (CO) 12 ] ( 3 ), respectively. Complexes 1 , 2 and 3 have been characterized by elemental analysis, spectroscopy and the crystal structures of 1 and 2 have been determined by X-ray crystallography. The structures of 1 and 2 contain a penta-nuclear M–Fe–S core, [Fe 2 S 2 MS 2 Fe 2 ] z − (M=V, z =0 ( 1 ) and M=Mn, z =2 ( 2 )), consisting of two [Fe 2 S 2 ]-units chelating to a metal atom. The two [Fe 2 S 2 ] units are in ‘butterfly’ type configuration like the one in [Fe 2 S 2 (CO) 6 ] 2− . In 1 there are four V–Fe bonds of 2.822–2.865 A, but in 2 there were no Mn–Fe bonds found. V–S distances are 2.205–2.210 A and Mn–S bond lengths are 2.358–2.380 A. The novel structural configuration, IR spectra and synthesis were discussed.

Theoretical studies on hyperpolarizabilities and UV-vis-IR spectra of a diamminecobalt(III) tetripeptide transition-metal complex

The second-order polarizabilities and the UV-vis-IR spectra of a transition-metal complex Co(NH3)2(L-ala–gly–gly) have been studied by using the MP2 and TDHF methods. The complex has a maximum β component in the direction from the N(alanyl) group to the N(glycyl) groups. A transparent optical spectrum region from 0.55 to 5.5 µm was found, which offers potential applications as an optical material. The alkyl substitution of the glycyl group only slightly affected the β value and retained the IR transparent region but may cause the molecules to have a favorite packing fashion in the bulk crystal that leads to larger second-order nonlinear optical coefficients.

A theoretical study on the second-order nonlinear optical susceptibilities of lithium formate monohydrate crystal, HCOOLi . H2O

Abstract Ab initio calculations of the first hyperpolarizabilities of (HCOOLi·H 2 O) 2 n supermolecules, as the building-blocks of lithium formate monohydrate (LFM) crystal with extended system, were performed for the first time. The dependence of the static β ijk 0 values on chain length was explored, and the frequency dependence of β ijk (−2 ω ; ω , ω ) was measured, and the influences of electron correlation and basis set on β ijk 0 were evaluated. Finally, we predicted the second-order nonlinear optical coefficients of LFM crystal. The β ijk 0 value of (HCOOLi·H 2 O) 2 n is linearly dependent on the chain length of supermolecule, which is quite unusual for an extended system connected by the O–Li bonds with ionic characters. Although the static component of β zzz 0 tensor is the static largest in these three components under study, the absolute value of frequency-dependent β zyy (−2 ω ; ω , ω ) element, transforming the smallest into the largest, is the most sensitive to frequency. After the fundamental wavelength is smaller than 500 nm, it is found that the β ijk (−2 ω ; ω , ω ) value is resonantly enhanced to a great extent due to the double frequency lies in the region of resonance. In addition, the β zxx 0 value goes from negative to positive with changes of electron correlation and basis set. Obviously, it is very necessary to take into account the effect of electron correlation, if the hyperpolarizability tensor components must be accurately calculated. Moreover, it is also very important whether it is adopted a complete basis set with diffuse and polarization functions. The calculated nonlinear coefficients at high level suggest that the scaled set reported by Robert seem more reasonable.