Kyrill Yu. Suponitsky

Applicability of hybrid density functional theory methods to calculation of molecular hyperpolarizability

The donor/acceptor (D/A) substituted pi-conjugated organic molecules possess extremely fast nonlinear optical (NLO) response time that is purely electronic in origin. This makes them promising candidates for optoelectronic applications. In the present study, we utilized four hybrid density functionals (B3LYP, B97-2, PBE0, BMK), Hartree-Fock, and second order Moller-Plesset correlation energy correction, truncated at second-order (MP2) methods with different basis sets to estimate molecular first hyperpolarizability (beta) of D/A-substituted benzenes and stilbenes (D=OMe, OH, NMe(2), NH(2); A=NO(2), CN). The results of density functional theory (DFT) calculations are compared to those of MP2 method and to the experimental data. We addressed the following questions: (1) the accurate techniques to compare calculated results to each other and to experiment, (2) the choice of the basis set, (3) the effect of molecular planarity, and (4) the choice of the method. Comparison of the absolute values of hyperpolarizabilities obtained computationally and experimentally is complicated by the ambiguities in conventions and reference values used by different experimental groups. A much more tangible way is to compare the ratios of betas for two (or more) given molecules of interest that were calculated at the same level of theory and measured at the same laboratory using the same conventions and reference values. Coincidentally, it is the relative hyperpolarizabilities rather than absolute ones that are of importance in the rational molecular design of effective NLO materials. This design includes prediction of the most promising candidates from particular homologous series, which are to be synthesized and used for further investigation. In order to accomplish this goal, semiquantitative level of accuracy is usually sufficient. Augmentation of the basis set with polarization and diffuse functions changes beta by 20%; however, further extension of the basis set does not have significant effect. Thus, we recommend 6-31+G(*) basis set. We also show that the use of planar geometry constraints for the molecules, which can somewhat deviate from planarity in the gas phase, leads to sufficient accuracy (with an error less than 10%) of predicted values. For all the molecules studied, MP2 values are in better agreement with experiment, while DFT hybrid methods overestimate beta values. BMK functional gives the best agreement with experiment, with systematic overestimation close to the factor of 1.4. We propose to use the scaled BMK results for prediction of molecular hyperpolarizability at semiquantitative level of accuracy.

Supramolecular step in design of nonlinear optical materials: Effect of π…π stacking aggregation on hyperpolarizability

Theoretical estimation of nonlinear optical (NLO) properties is an important step in systematic search for optoelectronic materials. Density functional theory methods are often used to predict first molecular hyperpolarizability for compounds in advance of their synthesis. However, design of molecular NLO materials require an estimation of the bulk properties, which are often approximated as additive superposition of molecular tensors. It is therefore important to evaluate the accuracy of this additive approximation and estimate the extent by which intermolecular interactions influence the first molecular hyperpolarizability β. Here we focused on the stacking aggregates, including up to 12 model molecules (pNA and ANS) and observed enhancement and suppression of molecular hyperpolarizability relative to the additive sum. We found that degree of nonadditivity depends on relative orientation of the molecular dipole moments and does not correlate with intermolecular interaction energy. Frenkel exciton model, based on dipole-dipole approximation can be used for qualitative prediction of intermolecular effects. We report on inaccuracy of this model for the molecules with long π-systems that are significantly shifted relative to each other, when dipole-dipole approximation becomes inaccurate. To obtain more detailed information on the effect of intermolecular interactions on β we proposed electrostatic approach which accounts for the mutual polarization of the molecules by each other. We measure the induced polarization of each molecule in the aggregate by the charge of its donor (or acceptor) group. The proposed approach demonstrates linear correlation β(FF) vs β(elm) (estimated by finite field theory and electrostatic model, respectively) and allows decomposition of the hyperpolarizability for a molecular aggregate into separate molecular contributions. We used this decomposition to analyze the reasons of deviation of aggregate β from additivity, as well as the cooperative effect of intermolecular interactions on hyperpolarizability for stacks of growing size. In cases of positive cooperativity (enhancement), we found 6-8 molecules to be necessary to reach the asymptotic limit. In more frequent cases of negative cooperativity two opposite factors play role. The first one consists of direct lowering of β due to repulsive dipole-dipole interactions. The second factor is originated in a decrease of molecular dipole moments, which in turn leads to a decrease of dipole-dipole repulsion, and therefore increases β. For strong intermolecular repulsive dipole-dipole interactions these effects nearly cancel each other. In such cases the trimers and even dimers are sufficient to reach the asymptotic limit of the infinite stacks. Based on the observed trends we estimated non-additive correction to β for well known NLO crystals NPAN and MNMA. In the case of NPAN, stacking effect on molecular hyperpolarizability represents the leading component of the crystal packing effect and improves the agreement between calculated and experimental data which is further improved when frequency dependence is taken in account.

Novel Highly Energetic Pyrazoles: N-Trinitromethyl-Substituted Nitropyrazoles.

A new family of energetic compounds, nitropyrazoles bearing a trinitromethyl moiety at the nitrogen atom of the heterocycle, was designed. The desirable high-energy dense oxidizers 3,4-dinitro- and 3,5-dinitro-1-(trinitromethyl)pyrazoles were synthesized in good yields by destructive nitration of the corresponding 1-acetonylpyrazoles. All of the prepared compounds were fully characterized by multinuclear NMR and IR spectroscopy, as well as by elemental analysis. Single-crystal X-ray diffraction studies show remarkably high density. Impact sensitivity tests and thermal stability measurements were also performed. All of the pyrazoles possess positive calculated heats of formation and exhibit promising energetic performance that is the range of 1,3,5-trinitroperhydro-1,3,5-triazine and pentaerythritol tetranitrate. The new pyrazoles exhibit positive oxygen balance and are promising candidates for new environmentally benign energetic materials.

Ionic Liquids as Unique Solvents in One‐Pot Synthesis of 4‐(N,2,2,2‐Tetranitroethylamino)‐3‐R‐Furazans

An efficient two-step one-pot protocol for the synthesis of N-nitrated trinitroethylamino furazans in an ionic liquid has been developed involving the condensation of aminofurazans with trinitroethanol and the N-nitration of an intermediate Mannich base. Trinitroethylnitramino derivatives have been synthesized and characterized by multinuclear NMR spectroscopy and X-ray crystallography. A role of the N,2,2,2-tetranitroethylamino group for stabilization of the high-density crystal-packing motif is described. The performance calculations gave detonation pressures and velocities for the furazan derivatives in a range of about 31-36 GPa and 8330-8745 ms(-1), respectively, which makes them competitive energetic materials. Furthermore, due to the positive oxygen balance, the compounds could be potential oxidizers for energetic formulations.

Novel trans-platinum complexes of the histone deacetylase inhibitor valproic acid; synthesis, in vitro cytotoxicity and mutagenicity.

The first examples of Pt complexes of the well known anti-epilepsy drug and histone deacetylase inhibitor, valproic acid (VPA), are reported. Reaction of the Pt(II) am(m)ine precursors trans-[PtCl(2)(NH(3))(py)] and trans-[PtCl(2)(py)(2)] with silver nitrate and subsequently sodium valproate gave trans-[Pt(VPA(-1H))(2)(NH(3))(py)] and trans-[Pt(VPA(-1H))(2)(py)(2)], respectively. The valproato ligands in both complexes are bound to the Pt(II) centres via the carboxylato functionality and in a monodentate manner. The X-ray crystal structure of trans-[Pt(VPA(-1H))(2)(NH(3))(py)] is described. Replacement of the dichlorido ligands in trans-[PtCl(2)(py)(2)] and trans-[PtCl(2)(NH(3))(py)] by valproato ligands (VPA(-1H)) to yield trans-[Pt(VPA(-1H))(2)(py)(2)] and trans-[Pt(VPA(-1H))(2)(NH(3))(py)] respectively, significantly enhanced cytotoxicity against A2780 (parental) and A2780 cisR (cisplatin resistant) ovarian cancer cells. The mutagenicity of trans-[Pt(VPA(-1H))(2)(NH(3))(py)] and trans-[Pt(VPA(-1H))(2)(py)(2)] was determined using the Ames test and is also reported.

Interaction of dichloride iron(II) clathrochelate with dimercaptomaleodinitrile: synthesis of the precursor monoribbed-functionalized phthalocyaninoclathrochelates and the unexpected formation of a new thiophene-containing heterocyclic system in the ribbed chelate fragment of the clathrochelate framework.

Clathrochelate iron(II) FeBd 2(S2C2(CN)2Gm)(BF)2 tris-dioximate with a ribbed vic-dinitrile fragment was synthesized as a precursor of the monoribbed-functionalized hybrid phthalocyaninoclathrochelates by nucleophilic substitution of the vic-dichloride FeBd2(Cl2Gm)(BF)2 clathrochelate (1) with the potassium salt of dimercaptomaleodinitrile. Reaction of nitromethane with this salt was followed by the condensation of the reaction products with 1 to yield the clathrochelate with an annulated previously unknown thiazinothiophene heterocyclic system in the ribbed fragment. Both complexes were characterized on the basis of elemental analysis; MALDI-TOF mass spectrometry; IR, UV-vis, (57)Fe Mössbauer, and NMR spectroscopies; and X-ray crystallography.

A Direct Approach to a 6-Hetarylamino[1,2,4]triazolo[4,3-b][1,2,4,5]tetrazine Library

The synthesis of 6-hetarylamino[1,2,4]triazolo[4,3-b][1,2,4,5]tetrazines is reported. The functionalized secondary amines were constructed via a K2CO3-mediated SNAr reaction of weakly basic hetarylamines with 3-(3,5-dimethylpyrazol-1-yl)[1,2,4]triazolo[4,3-b][1,2,4,5]tetrazines, which allowed displacement 3,5-dimethylpyrazolyl leaving group. Significantly, the reaction exhibited a broad substrate scope and proceeded in good yields.

A practical anodic oxidation of aminofurazans to azofurazans: an environmentally friendly route

Nickel oxyhydroxide, NiOOH, anode has been shown to be an effective tool for the oxidation of aminofurazans to azofurazans in ca. 1% aqueous alkali at room temperature. The electrochemical reaction is simple and convenient, eliminating the use of expensive and toxic organic or inorganic oxidants. The green economic preparation of desired azo compounds is very clean, producing only H2 as a result of cathodic reduction.

Inhibition of monoamine oxidase by indole-5,6-dicarbonitrile derivatives

Recent studies have found that phthalonitrile derivatives are remarkably potent inhibitors of human monoamine oxidase (MAO) A and B. In an attempt to further determine the structure-activity relationships (SARs) for MAO inhibition by this class of compounds and to discover novel potent MAO inhibitors, the present study investigated the MAO inhibition properties of a series consisting of indole-5,6-dicarbonitrile derivatives. The results document that 3-chloro-1H-indole-5,6-dicarbonitrile derivatives exhibited potent inhibition of the MAOs. For example, 3-chloro-2-(4-methylphenyl)-1H-indole-5,6-dicarbonitrile inhibited MAO-A and MAO-B with IC50 values of 0.014μM and 0.017μM, respectively. It was further shown that this compound acts as a reversible and competitive inhibitor of both MAO isoforms. An analysis of the SARs for MAO inhibition by 3-chloro-1H-indole-5,6-dicarbonitriles showed that methylation of the indole nitrogen eliminates MAO-B inhibition activity, and replacement of the 2-phenyl ring with the thienyl results in a 9-fold reduction of MAO-B inhibition activity. A series of 3-bromo-1-hydroxy-1H-indole-5,6-dicarbonitriles are, in turn, comparatively weaker MAO inhibitors. It may be concluded that indole-5,6-dicarbonitrile derivatives are suitable leads for the design MAO inhibitors for the treatment of disorders such as Parkinsons disease and depression.

Novel trinitroethanol derivatives: high energetic 2-(2,2,2-trinitroethoxy)-1,3,5-triazines

The multicomponent reaction of 2,4,6-trichloro-1,3,5-triazine with potassium trinitromethane and trinitroethanol was exploited for the first synthesis of the hetaryl trinitroethyl ether, 2,4-bis(2,2,2-trinitroethoxy)-6-trinitrometyl-1,3,5-triazine 13. The use of compound 13 as a scaffold for the synthesis of substituted trinitroethoxytriazine by sequential nucleophilic substitution processes is described. A number of trinitroethoxytriazines bearing a range of functional groups, including 2,4,6-tris(2,2,2-trinitroethoxy)-1,3,5-triazine 16, have been prepared. There has been no previous incorporation of the trinitroethoxy moiety to a heteroaromatic ring. All trinitroethoxytriazines were fully characterized using IR and multinuclear NMR spectroscopy, elemental analysis, and differential scanning calorimetry (DSC), and, in some cases, 16, 20 and 21, with single crystal X-ray structuring. When compared to the aliphatic trinitroethoxy compounds, the trinitroethoxytriazines show better energetic performance as calculated. The impact sensitivities and ignition points of the novel oxygen and nitrogen-rich triazines were measured. The ability of the applied trinitroethoxytriazines in solid composite propellants as well as in gas generant compositions for airbag inflators was evaluated. The straightforward preparation of these ethers highlights them as valuable new environmentally friendly and high-performing nitrogen and oxygen-rich materials.