3-(3’-吡啶基)-6-芳基-1,2,4-三唑并[3,4-b]-1,3,4-噻二唑衍生物基态和激发态性质

用密度泛函B3LYP方法对3-(3’-吡啶基)-6-芳基-1,2,4-三唑并[3,4-b]-1,3,4-噻二唑衍生物(芳基为苯基、3-吡啶基和苯乙烯基)进行基态几何构型全优化, 计算分子的电离势IP和电子亲和势EA等相关能量, 并用Zerner间略微分重叠(ZINDO)和含时密度泛函(TDDFT)方法计算吸收光谱, 用单组态相互作用方法(CIS)优化三种化合物分子的S1激发态结构, 分析其能量与发射光谱的关系, 计算溶剂中分子的吸收和发射光谱, 并与实验结果对照. 计算结果表明, 从3-(3’-吡啶基)-6-苯基-1,2,4-三唑并[3,4-b]-1,3,4-噻二唑分子(化合物A)到3-(3’-吡啶基)-6-(3’-吡啶基)-1,2,4-三唑并[3,4-b]-1,3,4-噻二唑分子(化合物B)以及3-(3’-吡啶基)-6-对乙烯苯基-1,2,4-三唑并[3,4-b]-1,3,4-噻二唑分子(化合物C)的电子亲和势依次增大, 愈来愈容易接受电子, 吸收光谱和发射光谱红移.     

3-(3′-吡啶基)-6-芳基-1，2，4-三唑并[3，4-b]-1，3，4-噻二唑衍生物基态和激发态性质

用密度泛函B3LYP方法对3-(3'-吡啶基)-6-芳基-1,2,4-三唑并[3,4-b]-1,3,4-噻二唑衍生物(芳基为苯基、3-吡啶基和苯乙烯基)进行基态几何构型全优化,计算分子的电离势I_p和电子亲和势E_A等相关能量,并用Zerner间略微分重叠(ZINDO)和含时密度泛函(TDDFT)方法计算吸收光谱,用单组态相互作用方法(CIS)优化三种化合物分子的S_1激发态结构,分析其能量与发射光谱的关系,计算溶剂中分子的吸收和发射光谱,并与实验结果对照.计算结果表明,从3-(3'-吡啶基)-6-苯基-1,2,4-三唑并[3,4-b]-1,3,4-噻二唑分子(化合物A)到3-(3'-吡啶基)-6-(3'-吡啶基)-1,2,4-三唑并[3,4-b]-1,3,4-噻二唑分子(化合物B)以及3-(3'-吡啶基)-6-对乙烯苯基-1,2,4-三唑并[3,4-b]- 1,3,4-噻二唑分子(化合物C)的电子亲和势依次增大,愈来愈容易接受电子,吸收光谱和发射光谱红移.     

Electronic and structural properties of A Al2Se4 (A=Ag, Cu, Cd, Zn) chalcopyrite semiconductors

We have studied the structural and electronic properties of defect chalcopyrite semiconductors A Al₂Se₄ (A=Ag, Cu, Cd, Zn) using density functional theory (DFT) based first principle technique within tight binding linear muffin-tin orbital (TB-LMTO) method. Our calculated structural parameters such as lattice constants a and c, tetragonal distortion (η=c/2a) are in good agreement with experimental work. Anion displacement parameters, bond lengths and bulk modulus are also calculated. Our band structure calculation suggests that these compounds are direct band gap semiconductors having band gaps 2.40, 2.50, 2.46 and 2.82 eV for A Al₂Se₄ (A=Ag, Cu, Cd, Zn) respectively. Calculated band gaps are in good agreement with other experimental and theoretical works within LDA limitation. We have made a quantitative estimation of the effect of p-d hybridization and structural distortion on the electronic properties. The reduction in band gap due to p-d hybridization is 19.47%, 21.29%, 0% and 0.7% for A Al₂Se₄ (A=Ag, Cu, Cd, Zn) respectively. Increment of the band gap due to structural distortion is 11.62%, 2.45%, 2.92% and 9.30% in case of AgAl₂Se₄, CuAl₂Se₄, CdAl₂Se₄ and ZnAl₂Se₄ respectively. We have also discussed the bond nature of all four compounds.     

O deficiency in the rutile TiO2 (110) surface: Ab initio quantum chemical investigation of the electronic properties

The (110) surface of rutile TiO₂ (110) has been modeled using a density functional theory (DFT) plane‐wave pseudo‐potential method (CASTEP). In this study, 6 and 9 atomic‐layer slabs have been examined. The stoichiometric surface converges to a low‐spin solution in both cases with a density of states (DOS) similar to that for the bulk. O deficiencies are introduced by the removal of neutral O atoms thus leaving a neutral model with a surfeit of 2 e^? per vacancy. This results in the partial filling of the Ti t_2g conduction band orbitals and a compensatory shift in the Fermi level. The reduced surface converges to a high‐spin solution in all cases, with the excess spin located within the previously unoccupied Ti t_2g orbitals. Removal of the bridging surface O atoms results in an excess spin of 2 electrons per unit cell with approximately one‐half that for removal of in‐plane surface O atoms and subsurface O atoms. The removal of O atoms from the surface leads to an increase of the band gap, with the largest increase due to the removal of in‐plane 3‐fold coordinated surface O atoms, and the smallest one due to the removal of subsurface O atoms. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006     

A comparative study of key properties of glycine glycinium picrate (GGP) and glycinium picrate (GP): A combined experimental and quantum chemical approach

Using experimental and computational techniques, a comparative study of electro-optical properties for glycine glycinium picrate (GGP) and glycinium picrate (GP) compounds has been performed. The single crystal of GGP has been grown using slow evaporation technique that was further subjected to experimental characterization of its electro-optical properties. The good optical transparency and mechanical strength at micro level was confirmed from optical and nanoindentation measurements using the Oliver–Pharr method of the grown single crystals. Differential scanning calorimetric (DSC) analysis was done to probe the thermal stability of the grown single crystals. Using the density functional theory (DFT) methods, we have not only investigated the GGP but also proposed GP molecule. Additionally, we have shed light on the molecular geometries, infrared and Raman spectra, linear and nonlinear optical properties of both GGP and GP at molecular level. The time dependent DFT (TD-DFT) approach was adopted to calculate the excitation energies of the molecules in different phases including gas, water, acetone, cyclohexane and chloroform as well. For GGP, its wavelength of maximum absorption is calculated to be ～390 nm at B3LYP/6-31G¹ level of theory. The calculated amplitudes of first hyperpolarizability (β_tot) for GGP and GP are found to be 712 and 970 a. u., respectively, which are about 16 and 23 times larger than that of the urea molecule (a prototype NLO molecule). Thus the present study not only brings to limelight the optical and nonlinear optical properties of GGP but also sheds light on the possible potential of GP as new NLO molecule.     

Crystal structure and quantum chemical investigation of 4-(3,4-dichlorphenyl)-1,2,4-triazole

1,2,4-Triazole derivative substituted in the 4th position — 4-(3,4-dichlorphenyl)-1,2,4-tirazole — has been synthesized. Crystal and molecular structure of the compound were determined by single crystal X-ray diffraction. Molecular geometry optimization and effective charge calculations were performed by DFT methods.     

Nonaqueous capillary electrophoresis and quantum chemical calculations applied to investigation of acid–base and electromigration properties of azahelicenes

Nonaqueous capillary electrophoresis (NACE) using methanol (MeOH) as a solvent of the BGEs and quantum mechanical density functional theory (DFT) have been applied to determine the thermodynamic acidity (ionization) constants (pK_a) of mono- and diaza[5]helicenes, mono- and diaza[6]helicenes, and their dibenzo derivatives in MeOH and water. First, the mixed acidity constants, , of ionogenic pyridinium groups of azahelicenes and their derivatives in MeOH were obtained by nonlinear regression analysis of pH dependence of their effective electrophoretic mobilities. The effective mobilities were measured by NACE in a large series of methanolic BGEs within a wide conventional pH range (pH_MeOH 1.6–12.0) and at ambient temperature (21–26°C) in a home-made CE device. Prior to mixed acidity constant calculation, the effective mobilities were corrected to reference temperature (25°C) and constant ionic strength (25 mM). Then, the mixed acidity constants were recalculated to the thermodynamic acidity constants pK_a,MeOH by the Debye–Hückel theory of nonideality of electrolyte solutions. Finally, from the methanolic thermodynamic pK_a,MeOH values, the aqueous thermodynamic constants were estimated using the empirical relations between methanolic and aqueous acidity constants derived for structurally related pyridine derivatives. Depending on the number and position of the nitrogen atoms in their molecules, the analyzed azahelicenes were found to be weak to moderate bases with methanolic pK_a,MeOH in the range 2.01–8.75 and with aqueous in the range 1.67–8.28. The thermodynamic pK_a,MeOH obtained by the DFT calculations were in a good agreement with those determined experimentally by NACE.     

Nitro group photoreduction of 4-(2-nitrophenyl)- and 4-(3-nitrophenyl)-1,4-dihydropyridines

The photoprocesses of nifedipine, a 4-(2-nitrophenyl)-1,4-dihydropyridine, and nimodipine and nitrendipine, two 3-nitrophenyl Hantzsch-type analogues, were studied by steady-state and time-resolved methods. The intramolecular photoreduction of nifedipine into its nitrosophenyl product takes place within a few ns. The quantum yield of conversion is Φ_red = 0.3 and does not depend significantly on the oxygen concentration and solvent properties. Formation of the fully reduced 4-(2-aminophenyl)-1,4-dihydropyridine as minor product is indicated by fluorescence spectroscopy. The photoreduction of nimodipine and nitrendipine is inefficient, Φ_red = 0.002 in acetonitrile, but markedly enhanced in the presence of donors such as triethylamine (TEA) and 2-propanol, e.g. for TEA Φ_red is up to 0.03. The triplet states of nimodipine and nitrendipine were characterized. They react intermolecularly with TEA and 2-propanol, forming radicals as intermediates and eventually several reduction products.     

Molecular modeling of 3,4-pyridinedicarbonitrile dye sensitizer for solar cells using quantum chemical calculations

The geometries, electronic structures, polarizabilities, and hyperpolarizabilities of organic dye sensitizer 3,4-pyridinedicarbonitrile was studied based on Hartree–Fock (HF) and density functional theory (DFT) using the hybrid functional B3LYP. Ultraviolet–visible (UV–Vis) spectrum was investigated by time dependent DFT (TD-DFT). Features of the electronic absorption spectrum in the visible and near-UV regions were assigned based on TD-DFT calculations. The absorption bands are assigned to π → π1 transitions. Calculated results suggest that the three lowest energy excited states are due to photoinduced electron transfer processes. The interfacial electron transfer between semiconductor TiO₂ electrode and 3,4-pyridinedicarbonitrile is due to electron injection process from excited dye to the semiconductor’s conduction band. The role of cyanine in 3,4-pyridinedicarbonitrile in geometries, electronic structures, and spectral properties were analyzed.     

Synthesis and Crystal Structure of 2-Amino-3-cyano- 4-（3,4-dimethoxyphenyl）-4H-benzo[h]chromenes

1INTRODUCTION4H-Chromeneisaconstructionunitofsomenaturalproducts.4H-Chromeneswithaminoandcyanogroupsarealsosynthonofsomespecialnaturalproducts[1,2].Thesubstituted4H-chromenespossessawiderangeofpharmacologicalactivi-ties[3～5].Inordertoinvestigatetheactivi…     

In-depth insight into the electronic and steric effects of phosphine ligands on the mechanism of the R-R reductive elimination from (PR3)2PdR2

The aim of this study was to investigate both the electronic and steric effects of the ancillary phosphine ligand L on the reductive elimination of Me-Me from a series of L₂PdMe₂ and LPdMe₂ complexes. Density functional theory was used to study these processes with the model ligands L = PMe₃, PH₃, PCl₃ and with the experimentally reported ligands L = PPh₃, PPh₂Me, PPhMe₂. For the model ligands we confirm that electron donation from L affects the barrier for reductive elimination from L₂PdMe₂ but not from LPdMe₂. In the former case the greater the electron donation or basicity of L, the greater the barrier and the later the transition state. This is because electron donation increases the σ^∗ antibonding between Pd and L in the transition structure. On the other hand, if L is a good π acceptor this stabilizes the occupied d_π orbital of Pd in the transition structure and lowers the barrier to reductive elimination. In the case of the reactions involving LPdMe₂ as the intermediate, it is the loss of the first L (L₂PdMe₂ → LPdMe₂ + L) which determines the differences in the barrier height. Greater electron donation leads to greater L-to-Pd σ donation and a stronger Pd-L bond, and thus a greater overall barrier. A comparison of these results with the reductive elimination of 1,3-butadiene from divinyl palladium complexes L₂PdR₂ shows that the barriers are lower in the vinyl case because of a mix of orbital factors. Our results show that there is a significant stabilizing interaction between the Pd d_π orbital and the vinyl-vinyl hybrid σ^∗/π^∗ orbitals in the reductive elimination transition structure. At the same time this Pd-R₂ orbital stabilization alleviates the potential antibonding interactions between Pd and L and makes the vinyl elimination much less susceptible to ancillary ligand effects. Energy-decomposition analyses have been used to elucidate the contributing factors to the activation energies for the reductive eliminations with the model phosphine ligands. These analyses have also been used to disentangle the electronic and steric effects involved in the larger ligand systems. The electronic effects of the experimentally reported ligands are found to be very similar to each other. On the other hand, steric effects lead to a destabilization of the reactant L₂PdMe₂ complexes but not the transition structures, which results in a decrease in the barriers to reductive elimination compared to the smaller phosphine ligands. These steric effects do not play a role in reductive elimination from LPdMe₂. These detailed analyses of the electronic and steric factors may be used to assist the design of systems which enhance or retard reductive elimination behaviour.     

Geometry,Electronic Structure,and Related Properties of Dye Sensitizer： 3,4-bis[1- （carboxymethyl）-3-indolyl]- 1 H-pyrrole-2,5-dione

The geometry, electronic structure, polarizability and hyperpolarizability of dye sensitizer 3,4-bis[1-（carboxymethyl）-3-indolyl]-1H-pyrrole-2,5-dione （BIMCOOH） were studied using density functional theory （DFT） with hybrid functional B3LYP, and the electronic absorption spectra were investigated using semi-empirical quantum chemical method ZINDO-1 and time-dependent DFT （TDDFT）. The results of natural bond orbital suggest that the natural charges of the dione, indole, and acetic groups are about 0.15e, -0.29e, and 0.44e, respectively. The calculated isotropic polarizability, polarizability anisotropy invariant and hyperpolarizability are 305.4, 188.3, and 1155.4 a.u., respectively. The electronic absorption spectral features in visible and near-UV region were assigned to the π→π^＊ transition due to the qualitative agreement between the experiment and the TDDFT calculations, and the transitions of the excited states 9-11 related to photoinduced intramolecular charge transfer processes. The analysis of electronic structure and UV-Vis absorption indicates that the indole groups primarily contributed sensitization of photo-to-currency conversion processes, and the interracial electron transfer between semiconductor TiO2 electrode and dye sensitizer BIMCOOH are electron injection processes from excited states of the dyes to the semiconductor conduction band.     

Synthesis and Crystal Structure of 2-Amino-3-cyano-4-(3,4-dimethoxyphenyl)-4H-benzo[h]chromenes

The title compound (C22H18N2O3) has been synthesized by the reaction of 3,4-dimethoxybenzaldehyde,malononitrile and 1-naphthol in ethanol in the presence of piperidine,and its structure was characterized by elemental analysis,IR,1H NMR and X-ray single-crystal diffraction.The crystal belongs to monoclinic,space group C2/c with a=24.221(6),b=9.016(2),c=17.003(5)A,β=93.16(1)°,V=3707(2)A3,Mr=358.38,Z=8,Dc=1.284g/cm3,μ(MoKα)=0.087mm-1,F(000)=1504,the final R=0.0432 and wR=0.1085.X-ray analysis reveals that the atoms of C(1),C(2),C(3),C(4),C(5) and O(1) form a boat-form six-membered ring in which the C(1)-C(2)(1.349(3)A) is a C=C double bond.     

(CH2)2N和(CH3)2NH+的密度泛函理论计算

用密度泛函理论UB3LYP／6-31G（d,p）方法研究了二甲胺自由基（CH3）2N及其质子化离子（CH3）2NH 的构象和超精细结构．在由构象研究得到的两种自由基的最稳定结构上,用密度泛函的UB3LYP和UB3PW91方法及从头计算的UHF、UMP2（FULL）方法计算了α-质子、β-质子和N核上的超精细偶合常数A（Hα）、A（Hβ）和A（N）结果表明：两种自由基中甲基内旋转的位垒均很低,分别为0．46kJ·mol-1（（CH3）2NH ）和2．6kJ·mol-1（（CH3）2N）．UB3LYP／6-31G（d,p）和UB3PW91／6-31G（d,p）计算的A（Hα）、A（Hβ）和A（N）与ESR实验结果符合得很好,UMP2／6-31G（d,p）方法的计算值与实验值符合得也较好．     

Structures of 1-（3,4-Dihydroxyphenyl）-2-（3,4-dimethoxyphenyl） ethanone and Its Hydrate Complex

The title compounds, C16H16O5 (I) and C16H16O5·H2O (II), were structurally characterized by single-crystal X-ray diffraction. Compound I crystallizes in monoclinic space group P21/c with a = 10.5574(10), b = 8.3576(9), c = 16.5528(16) , β = 91.762(3)°, Z = 4, R = 0.0524 and wR = 0.1084. The molecules are jointed into a chain by intermolecular O-H···O and C-H···O hydrogen bonds, which form layers parallel to (001). The chains run along the [110] and [110] directions alternatively layer by layer, and are assembled into a network by intermolecular O-H···O (carboxyl) hydrogen bonds. On the other hand, the hydrate complex (II) crystallizes in the triclinic space group P1 with a = 5.1451(2), b = 10.4583(4), c = 14.8267(5) , α = 70.900(2), β = 82.478(2), γ = 81.359(2)°, Z = 2, R = 0.0393 and wR = 0.0983. The molecules are linked into infinite two-dimensional ribbons by O-H···O (carbonyl) and solvent-bridged O-H···O hydrogen bonds.     

有机荧光分子2-氰基-3-(3, 4-二甲氧基苯基)-2-丙烯酰胺的可逆压致变色和质子刺激响应性能

设计合成了3-芳基-2-腈基丙烯酰胺类有机发光小分子2-氰基-3-(3, 4-二甲氧基苯基)-2-丙烯酰胺(CDMPA)。经研究发现, CDMPA化合物具有明显的压致变色和酸致变色现象。在外力刺激下,化合物CDMPA荧光最大发射峰发生20 nm的红移,经过加热或蒸汽处理后可恢复初始状态。对样品研磨前后粉末的X射线衍射图谱及荧光寿命衰减曲线进行测试分析得出, CDMPA压致变色现象归因于分子构型由晶态到无定形态的转化。另外,在酸刺激下CDMPA发光颜色由蓝光红移至黄光,最大发射波长红移33 nm。经过二甲基甲酰胺(DMF)处理后可恢复到初始状态。由测试得到的红外光谱及分子轨道理论计算推测,酸致变色现象是由氨基取代基的质子化影响了CDMPA前线分子轨道引起的。本研究可使人们深入了解这种类型材料的多刺激响应发光机制,且显著的颜色变化性能使CDMPA在传感器和检测装置方面具有潜在的应用前景。     

Theoretical Exploration of Stereochemical Nonrigidity for RfCo（PF3）x（CO）4-x（Rf=CF3, C2F5, C3F7, x=0-4）

The stereochemical nonrigidity of RfCo（PF3）x（CO）4-x（Rf=CF3,C2F5,C3F7,x=0-4） was studied at the theoretical level of B3LYP/6-31 1＋G^＊ via Gaussian 09.The intramolecular rearrangements in these penta-coordinated compounds are mainly caused by the vibrations of perfluoroalkyl groups.All the barriers along the reaction coordinate are less than 66.9 kJ/mol,which indicates that the rearrangements are kinetically favorable and hard to elucidate by experiment.Besides,ligand PF3 is a ligand similar to CO,the energy difference between the reactant and product is small.