Ab Initio and Density Functional Study on the First Hyperpolarizabilities of Squaric Acid Homologues

The first hyperpolarizabilities of four squaric acid homologues: squaric acid, 1,2-dithiosquaric acid,1,2-diselenosquaric acid and 1,2-ditellurosquaric acid have been calculated using ab initio and DFT methods. The effects of equilibrium geometries, basis set and electron correlation on the first hyperpolarizabilties of these molecules were investigated. The frequency dispersion effect and solvent effect, which are essential to get reliable outputs in comparison to the experimental results, have also been explored. On the basis of these investigations, it is worthy to point out that the heavy atom effect takes effect for these squaric acid homologues.     

Ab initio and density functional theory studies of the structure,gas-phase acidity and aromaticity of tetraselenosquaric acid

Results of ab initio self-consistent-field (SCF) and density functional theory (DFT) calculations of the gas-phase structure,acidity (free energy of deprotonation,G0) and aro-maticity of tetraselenosquaric acid (3,4-diselenyl-3-cy-dobutene-1,2-diselenone,H2C4Se4) are reported.The global minimum found on the potential energy surface of tetraselenosquaric acid presents a planar conformation.The ZZ iso-mer was found to have the lowest energy among the three planar conformers and the ZZ and ZE isomers are very dose in energy.The optimized geometric parameters exhibit a bond length equalization relative to reference compounds,cyclobu-tanediselenone,and cydobutenediselenol.The computed aromatic stabilization energy (ASE) by homodesmotic reaction is -77.4 (MP2(fu)/6 - 311 G //RHF/6 - 311 G) and - 54.8 kJ/mol (B3LYP/6 - 311 G //B3LYP/6 -311 G).The aromaticity of tetraselenosquaric add is indicated by the calculated diamagnetic susceptibility exaltation (A) - 19.13 (CSGT(IGAEM) - RHF/6 - 311 G// RHF/6-     

Theoretical predictions of the structure, gas-phase acidity and aromaticity of 1,2-diseleno-3,4-dithiosquaric acid

Results of ab initio self-consistent-field (SCF) and density functional theory (DFT) calculations of the gas-phase structure, acidity (free energy of deprotonation, ΔG^o), and aromaticity of 1,2-diseleno-3,4-dithiosquaric acid (3,4-dithiohydroxy-3-cyclobutene-1,2-diselenone, H₂C₄Se₂S₂) are reported. The global minimum found on the potential energy surface of 1,2-diseleno-3,4-dithiosquaric acid presents a planar conformation. The ZZ isomer was found to have the lowest energy among the three planar conformers and the ZZ and ZE isomers are very close in energy. The optimized geometric parameters exhibit a bond length equalization relative to reference compounds, cyclobutanediselenone, and cyclobutenedithiol. The computed aromatic stabilization energy (ASE) by homodesmotic reaction (Eq 1) is −20.1 kcal/mol (MP2(fu)/6-311+G** //RHF/6-311+G**) and −14.9 kcal/mol (B3LYP//6-311+G**//B3LYP/6-311+G**). The aromaticity of 1,2-diseleno-3,4-dithiosquaric acid is indicated by the calculated diamagnetic susceptibility exaltation (Λ) −17.91 (CSGT(IGAIM)-RHF/6-311+G**//RHF/6-311+G**) and −31.01 (CSGT(IGAIM)-B3LYP/6-311+G**//B3LYP/6-311+G**). Thus, 1,2-diseleno-3,4-dithiosquaric acid fulfils the geometric, energetic and magnetic criteria of aromaticity. The calculated theoretical gas-phase acidity is ΔG^o _1(298K)=302.7 kcal/mol and ΔG^o _2(298K)=388.4 kcal/mol. Hence, 1,2-diseleno-3,4-dithiosquaric acid is a stronger acid than squaric acid(3,4-dihydroxy-3-cyclobutene-1,2-dione, H₂C₄O₄). Received: 11 April 2000 / Accepted: 7 July 2000 / Published online: 27 September 2000     

Photochromic Dihetarylethenes. 8. A Novel Route to the Synthesis of 3,4-Bis(2,5-dimethyl-3-thienyl)furan-2,5-dione as a Potential Photochrome

There is proposed, and in the case of 2,5-dimethylthiophene carried out, a novel route to the synthesis of 3,4-dithienylfuran-2,5-dione type photochromes. This is done in two stages, the first being a Friedel-Crafts reaction of the starting thiophene with the dichloride of squaric acid and the second is a Baeyer-Villiger oxidation of the 3,4-bis(2,5-dimethyl-3-thienyl)cyclobutenedione to give the target 3,4-bis(2,5-dimethyl-3-thienyl)furan-2,5-dione.     

固态类杂芪分子一阶超极化率测定及溶剂效应

用溶致变色法研究溶剂对反式－（４－Ｎ,Ｎ－二甲氨基）－（４－Ｎ－甲基吡啶基）杂芪碘（ＤＡＳＰＩ）、反式、（２－Ｎ－比咯基）－（４－Ｎ－甲基吡啶基）杂芪碘３＊（ＭＰＰＳＩ）,反式－２（２－吡咯基）－２（４－Ｎ－比啶基）杂芪磺（ＰＰＳＩ）、反式－（２－呋喃基）－（４－Ｎ＿甲基吡啶基）杂芪碘（ＦＰＳＩ）、反式－（２－噻吩基）－（４－Ｎ－甲基吡啶基）杂芪磺（ＴＰＳＩ）和反式＿４－Ｎ－Ｌ在吡啶基）杂芪碘（Ｐ     

Role played by the organometallic fragment on the first hyperpolarizability of iron–acetylide complexes: A TD-DFT study

The static first hyperpolarizabilities (β) for a series of both substituted thiophene-acetylide ligands and the corresponding η⁵–monocyclopentadienyliron(II) complexes were determined by density functional theory (DFT) calculations. The effect on the hyperpolarizabilities by various donor and acceptor substituents in the thiophene-acetylide ligands was studied. The nature and role of the electronic excitation contributions to the first hyperpolarizability, using time-dependent DFT (TD-DFT) calculations, are rationalized in terms of the two-level model. Our calculations show that the organometallic fragment can form a very effective push-pull system in combination with electron-withdrawing substituents in the thiophene-acetylide moiety, leading to enhanced static first hyperpolarizabilities. Also, an improvement of the magnitude of β is expected if solvation effects are taken into account.     

First hyperpolarizability of polymethineimine with long-range corrected functionals

Using the long-range corrected (LC) density functional theory (DFT) scheme introduced by Iikura et al. [J. Chem. Phys. 115, 3540 (2001)] and the Coulomb-attenuating model (CAM-B3LYP) of Yanai et al. [Chem. Phys. Lett. 393, 51 (2004)], we have calculated the longitudinal dipole moments and static electronic first hyperpolarizabilities of increasingly long polymehtineimine oligomers. For comparison purposes Hartree-Fock (HF), Moller-Plesset perturbation theory (MP2), and conventional pure and hybrid functionals have been considered as well. HF, generalized gradient approximation (GGA), and conventional hybrids provide too large dipole moments for long oligomers, while LC-DFT allows to reduce the discrepancy with respect to MP2 by a factor of 3. For the first hyperpolarizability, the incorrect evolution with the chain length predicted by HF is strongly worsened by BLYP, Perdew-Burke-Ernzerhof (PBE), and also by B3LYP and PBE0. On the reverse, LC-BLYP and LC-PBE hyperpolarizabilities are correctly predicted to be positive (but for the two smallest chains). Indeed, for medium and long oligomers LC hyperpolarizabilities are slightly smaller than MP2 hyperpolarizabilities, as it should be. CAM-B3LYP also strongly improves the B3LYP results, though a bit less impressively for small chain lengths. The present study demonstrates the efficiency of long-range DFT, even in very pathological cases.     

Ligand-controlled First Hyperpolarizabilities of a Series of Tetrahedral Iridium Clusters Ir4（CO）9L： a TDDFT Study

A series of tetrahedral iridium carbonyl clusters coordinated by systematically varied series of ligands have been studied by TDDFT method focusing on their electronic and non- linear optical properties. The clusters of Ir4（CO）12 （1）, Ir4（μ-CO）3（CO）9 （2）, Ir4（μ-L）（CO）10 （L = dppm 3, dppe 4, （Ph2P）2CHMe 5, Ph2P（CH2）3PPh2 6） and Ir4（CO）10（phen） （phen = 1,10-phen- anthroline） （7） exhibit the first static hyperpolarizabilities of medium magnitude （βtot-10×10^-30 esu）. The second order nonlinear optical response of the seven clusters increase from 0 to 23 ×10^-30 esu; the high symmetric cluster Ir4（CO）12 debases its symmetry and presents the second order nonlinear optical behavior as the coordination style of some carbonyls changes to bridge style, and then the response increases regularly with the systematical variation of the ligands. The origination of the first hyperpolarizability is discussed by the expanded orbital decomposition scheme. The results suggest the d-d electron transition from the apical iridium atom to the other three Ir atoms inside the metal skeleton, and d-πelectron transitions from metals to carbonyls are responsible for the first hyperpolarizabilities. Particularly, for cluster 7, the charge transfer from d orbitals of iridium to π＊ orbirals of phenanthroline originates the first hyperpolarizabilities.     

含碱金属分子簇体系的结构和NLO性质

采用MP2方法优化得到Li(HF)n(n=2~4)体系的三个环型结构. 使用高水平的从头算方法MP2/6-311++G(3df,3pd)计算了它们的偶极矩μ0、极化率α0和一阶超极化率β0. 得出了大的一阶超极化率的变化规律, 并揭示出额外电子是引起大一阶超极化率的主要原因.     

Photochromic dihetarylethenes. 13. Optimization of conditions for the acylation of 2,5-dimethylthiophene with squaric acid dichloride

The conditions for acylation of 2,5-dimethylthiophene with squaric acid dichloride were optimized, and 3,4-bis(2,5-dimethylthiophen-3-yl)cyclobut-3-ene-1,2-dione was obtained in good yield. X-ray diffraction analysis demonstrated that the by-product has the structure of 1a,1b-dichloro-5-(2,5-dimethylthiophen-3-yl)-3-hydroxy-4,5a-dimethyl-1b,4a,5,5a-tetrahydro-1aH-1-thiacyclopropa[a]pentalen-2-one.     

VO2+ complexation by bioligands showing keto-enol tautomerism: a potentiometric, spectroscopic, and computational study

The interaction of VO(2+) ion with ligands of biological interest that are present in important metabolic pathways--2-oxopropanoic acid (pyruvic acid, pyrH), 3-hydroxy-2-oxopropanoic acid (3-hydroxypyruvic acid, hydpyrH), oxobutanedioic acid (oxalacetic acid, oxalH(2)), (S)-hydroxybutanedioic acid (l-malic acid, malH(2)), and 2,3-dihydroxy-(E)-butanedioic acid (dihydroxyfumaric acid, dhfH(2))--was described. Their complexing capability was compared with that of similar ligands: 3-hydroxy-2-butanone (hydbut) and 3,4-dihydroxy-3-cyclobutene-1,2-dione (squaric acid, squarH(2)). All of these ligands (except l-malic acid) exhibit keto-enol tautomerism, and the presence of a metal ion can influence such an equilibrium. The different systems were studied with electron paramagnetic resonance (EPR) and UV-vis spectroscopies and with pH potentiometry. Density functional theory (DFT) methods provide valuable information on the relative energy of the enol and keto forms of the ligands both in the gas phase and in aqueous solution, on the geometry of the complexes, and on EPR and electronic absorption parameters. The results show that most of the ligands behave like α-hydroxycarboxylates, forming mono- and bis-chelated species with (COO(-), O(-)) coordination, demonstrating that the metal ion is able to stabilize the enolate form of some ligands. With dihydroxyfumaric acid, the formation of a non-oxidovanadium(IV) complex, because of rearrangement of dihydroxyfumaric to dihydroxymaleic acid (dhmH(2)), can be observed. With 3-hydroxy-2-butanone and 3,4-dihydroxy-3-cyclobutene-1,2-dione, complexation of VO(2+) does not take place and the reason for this behavior is explained by chemical considerations and computational calculations.     

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.     

方酸的合成进展

介绍了方酸（３,４－二羟基－３－环丁烯－１,２－二酮）的各种合成方法,评述了有机化学、电化学、生物发酵等方法合成方酸的进展及应用前景,参考文献２９篇。     

锂掺杂胺化物中氮原子配位数效应对结构和非线性光学性质的影响

采用MP2／6—311＋＋G（d,p）方法得到了含有不同氮原子配位数的系列锂掺杂胺化物的几何结构,并使用MP2／6．311＋＋G（2d,p）方法计算了该系列的非线性光学性质．结果表明：相对于未掺杂体系,锂掺杂极大地增加了体系的一阶超极化率（β0）,其中1的β0值是掺杂前的3238倍;体系的风随着氮原子配位数的增加而显著增加,具有3个配位氮原子的1的风值达到2．8×10^5a．u．另外,频率依赖的一阶超极化率（β（-ω;ω,0）和β（-2ω;ω,0））也表现了同样的趋势．     

五元杂环分子超极化率的电子相关效应

用有限场方法在HF和MP4水平上计算呋喃、吡咯和噻吩的极化率、一阶和二阶超极化率.结果表明,电子相关效应对各阶极化率,尤其是高阶极化率影响较大.MP2计算值较HF有显著改善,一阶超极化率的MP2,MP3和MP4计算值依次增大,二阶超极化率的MP2和MP4值相近,而MP3值小于MP2.呋喃、吡咯和噻吩的各阶极化率在各级微扰中均具有与HF水平上一致的相对大小顺序.     

An ab Initio Study of Tetrathiosquaric Acid

Inthepastfewdecades,sincetheoxocarbonanionsC.O.'-wererecognizedasmembersofanewclassofstabilizedcarbocyclicnonbenzenoidaromaticcompounds"',theknowledgeoftheirchemicalandphysicalpropertieshasbeendevelopingrapidly'Theiruniqueelectronicstructures,highdegreeofsymmetry,andestheticallybeauti-fulgeometrygeneratedafreshimpetustostudytheeffectofreplacingtheoxygensbyvariousfunctionalgroups,suchassulfur',andselenium[11.Analogoustotheoxocar-bondianions,thethioxocarbondianionscanbecharacterizedbythegeneralf…     

Electronic and vibrational hyperpolarizabilities of alkali- and alkaline-earth-doped boron nitride nanotubes

This work reports the results of the vibrational corrections and frequency dependence to the first hyperpolarizabilities of the alkali- and alkaline-earth-doped boron nitride nanotubes. The electronic contributions were computed by means of the density functional theory with the M06-2X functional, and the vibrational corrections were calculated using the perturbation theoretical method and the field-induced coordinates methodology. The results for the electronic contribution show that such materials exhibit large first hyperpolarizabilities and electride characteristic. We also show that the distribution of the excess electron, which originates from the doping atoms, plays an important role in the large electronic hyperpolarizabilities (β^el). Moreover, our findings strongly indicate that the effect of vibrations on the hyperpolarizabilities can be quite important and can even be much larger than the electronic counterpart.     

Theoretical study on second-order nonlinear optical properties of 1,10-phenanthroline Ru(Ⅱ) complexes

The dynamic first hyperpolarizabilities of a series of 1,10-phenanthroline Ru(Ⅱ) complexes were carried out using density functional theory(DFT).The results indicate that these complexes have large second-order nonlinear optical(NLO) responses.Specially,complex 6b has a maximal first hyperpolarizability βtot value.The first hyperpolarizabilities can be tuned by changing the ancillary ligand,introducing electron-acceptor group NO2 and/or increasing π-conjugation on phenanthroline.Calculations on absorption spectra demonstrate that the second-order NLO responses of complexes in series a are ascribed to the intraligand charge transfer(ILCT),while the complexes in series b exhibit metal-to-ligand charge transfer(MLCT) and ligand-to-ligand charge transfer(LLCT) transition at relatively low-energy absorptions.     

Solid-state linear-dichroic infrared (IR-LD) spectroscopic and theoretical characterization of 2-[(2-ethoxy-3,4-dioxocyclobut-1-en-yl)amino]propanamide

2-[(2-Ethoxy-3,4-dioxocyclobut-1-en-yl)amino]propanamide (N-alaninamidoamide of squaric acid ethyl ester) has been characterized structurally and spectroscopically by ab initio calculations and IR-LD spectroscopy of oriented crystals suspended in a nematic liquid crystal. The results are compared with single crystal X-ray structures illustrating the possibilities of this experimental approach to obtaining structural information as well as assigning IR bands.