Theoretical study of photoinduced ring-isomerization in the 1,2,4-oxadiazole series

A theoretical study of photoinduced ring-isomerization of 3-amino-5-methyl- and 3-amino-5-phenyl-1,2,4-oxadiazoles is reported. The results well agree with the reported experimental data: in particular, they explain the ring-photoisomerization into the corresponding 2-amino-1,3,4-oxadiazoles through a ring contraction-ring expansion route; moreover, the occurrence of competing pathways involving both the ring contraction and the internal cyclization-isomerization mechanism during irradiation of the 5-alkyl substituted substrates in the presence of a base has been also substantiated.     

Theoretical study of the potential energy curves of the series of diatomic radicals MeIIX

The potential energy curves of some low lying electronic states of the diatomic radicals BeCl and MgF have been calculated. The calculation has been performed according to a stepwise procedure, outlined in a previous work. The potential energy curves are very similar to those of the mercury halide radicals, the electronic transitions of which can be employed for efficient laser apparatus.     

Theoretical study of radiationless deactivation of a series of coumarin derivatives

The electronic structures of a series of coumarin derivatives have been calculated by the INDO/S method. A dependence of the relative position of the lowest energy excited states with different orbital types and multiplicities on the length of the C=O bond has been observed for molecules which display thermal quenching of fluorescence. L. Ya. Karpov Physical Chemistry Research Institute, 10 Vorontsov Pole Ulitsa, 103064 Moscow, Russia. Poltava Department, Ukraine Academy of the Science of Technological Cybernetics, 3 Kovalya Ulitsa, 314069 Poltava, Ukraine. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 33, No. 2, pp. 105–110, March–April, 1997.     

Tautomerism of oxopyridines and oxopyrimidines: Theoretical study with complete optimization of geometry

The semiempirical MINDO /3 method is employed to calculate the energies of various tautomers of model tautomeric compounds— 2-oxo- and 4-oxopyridines and pyrimidines. The results are compared with experimental data in the gas phase, where the solute–solvent interactions not included in theoretical calculations are absent. Although the relative energies obtained by the MINDO /3 method appear to be superior to other semiempirical and ab initio calculations, the accuracy of the method was determined to be as low as 3–4 kcal/mol. It indicates that it is exceedingly difficult to account theoretically for intrinsic stabilities of the tautomers. The importance of various factors influencing calculated free-energy differences is discussed. Particular attention is paid to the problem of geometry optimization.     

Theoretical study of two-photon absorption properties of a series of ferrocene-based chromophores

The electronic structures, one-photon absorption (OPA), and two-photon absorption (TPA) properties of a series of ferrocene-based chromophores with TCF-type acceptors (TCF = 2-dicyanomethylene-3-cyano-4-methyl-2,5-dihydrofuran) have been studied by using the ZINDO-SOS method. The results have revealed that OPA and TPA of ferrocenyl derivatives are affected by the strength of the acceptor, especially the pi-bridge conjugation length. The TPA cross section increases with increasing acceptor strength and pi-bridge conjugation length. The TCF-type acceptor with a phenyl group can lead to a larger TPA cross section. Quadrupole molecules have the largest TPA cross sections (2000-3000 GM), which are about 4 times that of the corresponding dipolar molecules, indicating larger interactions between the top and bottom branches. Finally, the origins of the two-photon excitations for ferrocenyl derivatives are analyzed. The calculations show that ferrocenyl derivatives with TCF-type acceptors (especially quadrupole molecules) are promising candidates for TPA materials.     

Theoretical study on second-order nonlinear optical properties of unsymmetric bis (phenylethynyl) benzene series derivatives

On the basis of ZINDO methods, according to the sum-overstates (SOS) expression, the program for the calculation of the second-order nonlinear optical susceptibilities βijk and βμ of molecules was devised, and the structures and nonlinear optical properties of unsymmetric bis (phenylethynyl) benzene series derivatives were studied. The influence of the molecular conjugated chain lengths, the donor and the acceptor on βμ was examined.     

Theoretical study of the competition between various mechanisms of gas-phase decomposition in the series of primary N-nitramines

Nonempirical and density-functional methods were used to determine geometric parameters, enthalpies of formation of compounds and radicals, dissociation energies of the N-NO₂ bonds of primary N-nitramines and N,N-dinitramines. The tendencies toward variation of the geometric structure, enthalpies of formation, and dissociation energy in the series of primary N-nitramines were analyzed. Alternative mechanisms of the gas-phase thermal destruction to give experimentally observed reaction products were studied for the example of N-methylnitramine and its homologues.     

Synthesis of the complete series of mono acetates of N-acetyl-D-neuraminic acid

The short syntheses of each of the mono-acetates of N-acetyl-D-neuraminic acid are reported. These are important molecules for studying the mechanism and function of enzymes which utilise Neu5Ac as a substrate. However, until now these molecules were not available as pure compounds and instead had to be studied as mixtures. Neu4,5Ac(2) and Neu5,8Ac(2) were synthesised from a common precursor in 2 and 4 steps respectively, while Neu2,4Ac(2) and Neu5,7Ac(2) were synthesised in 3 and 4 steps respectively from another common precursor. Both precursors could be easily prepared in 3 steps from Neu5Ac itself. Importantly, no scrambling of the anomeric stereochemistry was detected throughout the course of these syntheses.     

Theoretical study on the protonation of AZA-aromatics

The protonation of azanaphthalenes and azabenzenes has been studied theoretically using CNDO/2 wavefunctions and perturbation theory in order to examine the correlation between pK_a values and quantum-mechanical quantities.[/p]     

Theoretical study on a series of push–pull molecules grafted on methacrylate copolymers serving for nonlinear optics

The B3LYP functional combined with 6‐31G(d) basis set have been designated as the most appropriate for structural investigations of a new range of organic conjugated push–pull molecules containing numerous electron donor/acceptor couples in their ends. Second‐order Møller Plesset has been used to properly reproduce nonlinear optical (NLO) properties and to study the alkyl chain length effect of these systems. Satisfactory dynamic hyperpolarizabilities at the wavelength 1064 nm are obtained with values in the order of 11,500 × 10^?30 esu. Then, the study has been extended to monomers generated by combination of the chromophores to either acryloyl chloride or 4‐hydroxy‐styrene sequences. Then, the obtained molecules have been grafted to a methyl methacrylate copolymeric chain, the resulting values of β(1064 nm) have been demonstrated to be sensitive to these modifications. © 2012 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

A novel series of iridium complexes with alkenylquinoline ligands: Theoretical study on electronic structure and spectroscopic property

The ground and the lowest-lying triplet excited state geometries, electronic structures, and spectroscopic properties of a novel series of neutral iridium(III) complexes with cyclometalated alkenylquinoline ligands [(C^N)₂Ir(acac)] (acac = acetoylacetonate; C^N = 2-[(E)-2-phenyl-1-ethenyl]pyridine (pep) 1; 2-[(E)-2-phenyl-1-ethenyl]quinoline (peq) 2; 1-[(E)-2-phenyl-1-ethenyl]isoquinoline (peiq) 3; 2-[(E)-1-propenyl]pyridine (pp) 4; 2-[(E)-1-fluoro-1-ethenyl]pyridine (fpp) 5) were investigated by DFT and CIS methods. The highest occupied molecular orbital is composed of d(Ir) and π(C^N) orbital, while the lowest unoccupied molecular orbital is dominantly localized on C^N ligand. Under the TD-DFT with PCM model level, the absorption and phosphorescence in CH₂Cl₂ media were calculated based on the optimized ground and triplet excited state geometries, respectively. The calculated lowest-lying absorptions at 437 nm (1), 481 nm (2), 487 nm (3), 422 nm (4), and 389 nm (5) are attributed to a {[d_x²-y²(Ir) + d_xz(Ir) + π(C^N)] → [π∗(C^N)]} transition with metal-to-ligand/intra-ligand charge transfer (MLCT/ILCT) characters, and the calculated phosphorescence at 582 nm (1), 607 nm (2), 634 nm (3), 515 nm (4), and 491 nm (5) can be described as originating from the ³{[d_x²-y²(Ir) + d_xz(Ir) + π (C^N)] [π∗(C^N)]} excited state with the ³MLCT/³ILCT characters. The calculated results revealed that the phosphorescent color of these new Ir(III) complexes can be tuned by changing the π-conjugation effect strength of the C^N ligand.     

新型非线性光学材料的分子设计: 系列螺旋共轭化合物的结构、光谱及二 阶非 线性光学性质的理论研究

采用AM1和ZINDO系列方法研究了螺旋共轭分子2,2'-螺二茚-1,1',3,3'-四酮及其腈基衍生物的几何构型,研究了各分子的稳定构型,并以稳定为基础,计算了这些分子的电子光谱,二阶非线性光学系数βμ,β0,及电荷转移,考察了取代基变化对βμ的影响,计算结果表明所设计分子兼具较大的二阶非线性光学系数和较高的透过率,有希望成为一类新型的二阶非线性光学材料。     

Theoretical study on the small carbon nano-ladders

1,3-Butadiyne, 1,3,5-hexatriyne, 1,3,5,7-octatetrayne, and 1,3,5,7,9-decapentayne are small oligomeric forms of acetylene. These oligomers participate in cyclization reactions to form ladder-like structures. Enthalpies, ?H, and Gibbs free energies, ?G, of the cyclization reactions were calculated employing MP2 and B3LYP methods. The calculated ?H and ?G were positive, and their variation versus carbon atoms number, n, was fitted in linear functions as ?H(n) = a+bn. The calculations were performed on the structures with carbon numbers up to 20. Also, consecutive cyclization reactions between acetylene molecules were studied. During these consecutive reactions, two different structures, zigzag-ladder-like and cyclic molecules with tetragonal rings, were produced. Among the cyclic structures, the hexagonal form was the most stable structure. The calculated ?H and ?G of formation of zigzag-ladder-like molecules were excellently fitted in linear functions. The obtained functions for ?H and ?G calculated by MP2 method are ?H(n) = 139.67?126.44n and ?G(n) = 80.987?75.684n, respectively.     

聚集诱导发光现象的理论研究

本文系统介绍了本课题组发展的分子辐射跃迁和无辐射跃迁速率常数的热振动关联函数理论方法的最新进展及其在聚集诱导发光领域的典型应用. 基于第一性原理计算, 定量考察了位阻、温度、聚集等因素对分子体系发光性质的影响. 从微观角度给出了分子聚集诱导发光机理： 分子激发态的无辐射能量衰减通道主要是对应于低频模式的芳香环扭转和高频模式的碳碳伸缩振动. 当位阻增加、温度降低或者分子聚集时, 芳香环的转动受限, 无辐射能量衰减通道被抑制, 导致无辐射跃迁速率常数降低, 而其对辐射跃迁速率常数影响不大, 从而提高分子的荧光量子产率, 荧光增强.     

Theoretical study on the unimolecular decomposition of thiophenol

The potential energy surface for the unimolecular decomposition of thiophenol (C(6)H(5)SH) is mapped out at two theoretical levels; BB1K/GTlarge and QCISD(T)/6-311+G(2d,p)//MP2/6-31G(d,p). Calculated reaction rate constants at the high pressure limit indicate that the major initial channel is the formation of C(6)H(6)S at all temperatures. Above 1000 K, the contribution from direct fission of the S-H bond becomes important. Other decomposition channels, including expulsion of H(2) and H(2)S are of negligible importance. The formation of C(6)H(6)S is predicted to be strong-pressure dependent above 900 K. Further decomposition of C(6)H(6)S produces CS and C(5)H(6). Overall, despite the significant difference in bond dissociation, i.e., 8-9 kcal/mol between the S-H bond in thiophenol and the O-H bond in phenol, H migration at the ortho position in the two molecules represents the most accessible initial channel.     

苯并噻二唑醇解反应机理的理论研究

苯并噻二唑（BTH）是新型植保制剂。预防对象包括白粉病、锈病、霜霉病等阻引。 为更好地了解BTH的环境行为，本文研究了BTH醇解反应机理及反应的动力学。     

金属碳笼(Met-Cars)化学反应的理论研究 2: Ti8C12与H2O,C2H4生成Ti8C12(H2O)8和Ti8C12(C2H4)4反应的ab initio研究

用量子化学从头计算方法, 研究了Ti8C12分别与H2O, C2H4作用形成Ti8C12(H2O)8, Ti8C12(C2H4)4的反应。计算结果表明, 在Ti8C12(H2O)8中, 电子由H2O向Ti8C12转移, 在Ti8C12(C2H4)4中, 电子由Ti8C12向C2H4转移。从Ti8C12生成Ti8C12(H2O)8能量降低, 稳定性增加, 生成Ti8C12(C2H4)4能量升高, 稳定性减小。