Margarita Cerón

Synthesis, optical, and spectroscopic characterisation of substituted 3-phenyl-2-arylacrylonitriles

The Knoevenagel condensation between aldehydes and substrates with active methylene groups was applied to synthesise a series of 3-(4-substituted phenyl)-2-arylacrylonitriles (aryl = phenyl or pyridyl). Chloro-, fluoro-, or dimethylamino-substituted aryls and a cyano group attached to the double bond of acrylonitrile were studied. Previous studies showed that the condensation products were E isomers. The compounds synthesised were: 3-(4-chlorophenyl)-2-phenylacrylonitrile, 3-(4-chlorophenyl)-2-(pyridin-2-yl)acrylonitrile, 3-(4-chlorophenyl)-2-(pyridin-3-yl)acrylonitrile, 3-(4-chlorophenyl)-2-(pyridin-4-yl)acrylonitrile, 3-(4-fluorophenyl)-2-phenylacrylonitrile, 3-(4-fluorophenyl)-2-(pyridin-2-yl)acrylonitrile, 3-(4-fluorophenyl)-2-(pyridin-3-yl)acrylonitrile, 3-(4-fluorophenyl)-2-(pyridin-4-yl)acrylonitrile, 3-(4-dimethylaminophenyl)-2-phenylacrylonitrile, 3-(4-dimethylaminophenyl)-2-(pyridin-2-yl)acrylonitrile, 3-(4-dimethylaminophenyl)-2-(pyridin-3-yl)acrylonitrile, and 3-(4-dimethylaminophenyl)-2-(pyridin-4-yl)acrylonitrile. Structures were confirmed by IR, MS, and NMR spectral data. Molar absorption coefficient, absorbance, and fluorescence emission spectra were compared in order to evaluate the effects of substituents on phenyl and the position of nitrogen in pyridine moiety on the electronic properties of acrylonitrile derivatives prepared.

Synthesis, Characterization and Photophysical Properties of Pyridine-Carbazole Acrylonitrile Derivatives

We synthesized three novel highly fluorescent compounds, 2-(2’-pyridyl)-3-(N-ethyl-(3’-carbazolyl))acrylonitrile, 2-(3”-pyridyl)-3-(N-ethyl-(3’-carbazolyl))acrylonitrile, and 2-(4-pyridyl)-3-(N-ethyl-(3’-carbazolyl))acrylonitrile by Knoevenagel condensation. The first two were synthesized without solvent in the presence of piperidine as a catalyst; the third was synthesized without a catalyst and with N,N-dimethylformamide as a solvent. In solution, the molar absorption coefficients showed absorptions at 380, 378, and 396 nm, respectively; in solid state, absorptions were at 398, 390, and 442 nm, respectively. The fluorescence emission was at 540, 540 and 604 nm, respectively, the 2-(4-pyridyl)-3-(N-ethyl-(3’-carbazolyl))acrylonitrile showed a red shift in the emission of 64 nm compared to the other two compounds. The fluorescence quantum yield for the compounds in powder form showed values of 0.05, 0.14, and 0.006, respectively; compared with the value measured for the Alq3 reference, 2-(3”-pyridyl)-3-(N-ethyl-(3’-carbazolyl))acrylonitrile had a lightly higher value. The third harmonic generation measurement for 2-(2’-pyridyl)-3-(N-ethyl-(3’-carbazolyl))acrylonitrile yielded a χ(3) value of 5.5 × 10−12 esu, similar to that reported for commercial polymers.

Theoretical and Experimental Spectroscopic Analysis of Cyano-Substituted Styrylpyridine Compounds

A combined theoretical and experimental study on the structure, infrared, UV-Vis and 1H NMR data of trans-2-(m-cyanostyryl)pyridine, trans-2-[3-methyl-(m-cyanostyryl)] pyridine and trans-4-(m-cyanostyryl)pyridine is presented. The synthesis was carried out with an efficient Knoevenagel condensation using green chemistry conditions. Theoretical geometry optimizations and their IR spectra were carried out using the Density Functional Theory (DFT) in both gas and solution phases. For theoretical UV-Vis and 1H NMR spectra, the Time-Dependent DFT (TD-DFT) and the Gauge-Including Atomic Orbital (GIAO) methods were used, respectively. The theoretical characterization matched the experimental measurements, showing a good correlation. The effect of cyano- and methyl-substituents, as well as of the N-atom position in the pyridine ring on the UV-Vis, IR and NMR spectra, was evaluated. The UV-Vis results showed no significant effect due to electron-withdrawing cyano- and electron-donating methyl-substituents. The N-atom position, however, caused a slight change in the maximum absorption wavelengths. The IR normal modes were assigned for the cyano- and methyl-groups. 1H NMR spectra showed the typical doublet signals due to protons in the trans position of a double bond. The theoretical characterization was visibly useful to assign accurately the signals in IR and 1H NMR spectra, as well as to identify the most probable conformation that could be present in the formation of the styrylpyridine-like compounds.

The effect of the supramolecular network of (Z)-3-(4-(diphenylamino)phenyl)-2-(pyridin-2-yl)-acrylonitrile on the fluorescence behavior of a single crystal: experimental and theoretical studies

The molecular structure and molecular interactions of an α,β-unsaturated nitrile, such as the interaction between adjacent molecules of (Z)-3-(4-(diphenylamino)phenyl)-2-(pyridin-2-yl)-acrylonitrile (Z-DPPyACN) throughout the 4-diphenylamino moiety with the phenyl and pyridyl rings, play an important role in the self-assembly behaviors and optical properties of its powder and single-crystal forms. The crystal packing exhibits multiple C–H⋯π and CH⋯HC edge-to-face interactions that contribute to the supramolecular network between adjacent molecules. The resulting molecular structure resembles a pinwheel which exhibits a strong emission intensity at three different wavelengths. The crystal belongs to the monoclinic space group P21/n, with dimensions a = 12.9551(2), b = 11.29300(15), c = 14.6992(3) A, β = 115.648(2)° and Z = 4. The single-crystal compound shows three emission maxima at 533, 569, and 607 nm, whereas the powder and the molecules in an aggregated state show maximum emission intensities that are dependent on the nature of the solvent. The Z-DPPyACN dyes optical properties show a Stokes shift caused by the reorganization of the molecule in the excited state, as effected by the solvent polarity. This indicates a large change in the dipole moment of dye molecules upon excitation due to an intramolecular charge transfer interaction. From a theoretical point of view, the molecular geometry, electronic structure, and excitation energies are reported using density functional theory and compared with the experimentally determined one photon absorption and emission spectra.

Changes in the luminescence emission of α,β-unsaturated acrylonitrile derivatives: morphology, polymorphism and solvent effect

We report an interesting and clear property–structure relationship between the emission wavelength and the morphologies of samples separated by evaporation using a sublimator and a solvent. The compounds are (Z)-3-(4-(dimethylamino)phenyl)-2-(pyridin-4-yl)acrylonitrile Z-DMPyACN (I) and (Z)-3-(4-(diphenylamino)phenyl)-2-(pyridin-2-yl)acrylonitrile Z-DPPyACN (II). I exhibits strong emission in the solid state, but not in a solution, whereas II exhibits emission in a solution and as a solid. Characterization by single-crystal X-ray crystallography showed that the Z-DMPyACN polymorph (Ii) has a monoclinic unit cell with a = 7.0445(2); b = 17.1474(5); c = 10.9776(4) A, and β = 107.251(4)° and is found in the space group P21/c with Z′ = 1. The orange crystal habit and color are different from the structure reported, (Z′ = 2, block and yellow). The Ii luminescence displayed an absorbance maximum at λmax = 427 nm and an emission maximum at λem = 555 nm. From the Z-DPPyACN II evaporation in the sublimator, three solids were recovered, featuring emission wavelengths that were dependent on the size of the particles (nanoparticles) rather than on the single-crystal structure. The IIg, IIy, and IIo powders showed emission maxima at λem = 546, 558, and 607 nm, respectively. Characterization was carried out by UV-vis, fluorescence and 1H-NMR in different polarity solvents, as well as SCXRD, PXRD and SEM.

Conformational and Molecular Structures of α,β-Unsaturated Acrylonitrile Derivatives: Photophysical Properties and Their Frontier Orbitals

We report single crystal X-ray diffraction (hereafter, SCXRD) analyses of derivatives featuring the electron-donor N-ethylcarbazole or the (4-diphenylamino)phenyl moieties associated with a -CN group attached to a double bond. The compounds are (2Z)-3-(4-(diphenylamino)-phenyl)-2-(pyridin-3-yl)prop-2-enenitrile (I), (2Z)-3-(4-(diphenylamino)phenyl)-2-(pyridin-4-yl)-prop-2-enenitrile (II) and (2Z)-3-(9-ethyl-9H-carbazol-3-yl)-2-(pyridin-2-yl)enenitrile (III). SCXRD analyses reveal that I and III crystallize in the monoclinic space groups P2/c with Z’ = 2 and C2/c with Z’ = 1, respectively. Compound II crystallized in the orthorhombic space group Pbcn with Z’ = 1. The molecular packing analysis was conducted to examine the pyridine core effect, depending on the ortho, meta- and para-positions of the nitrogen atom, with respect to the optical properties and number of independent molecules (Z’). It is found that the double bond bearing a diphenylamino moiety introduced properties to exhibit a strong π-π-interaction in the solid state. The compounds were examined to evaluate the effects of solvent polarity, the role of the molecular structure, and the molecular interactions on their self-assembly behaviors. Compound I crystallized with a cell with two conformers, anti and syn, due to interaction with solvent. DFT calculations indicated the anti and syn structures of I are energetically stable (less than 1 eV). Also electrochemical and photophysical properties of the compounds were investigated, as well as the determination of optimization calculations in gas and different solvent (chloroform, cyclohexane, methanol, ethanol, tetrahydrofuran, dichloromethane and dimethyl sulfoxide) in the Gaussian09 program. The effect of solvent by PCM method was also investigated. The frontier HOMO and LUMO energies and gap energies are reported.

Synthesis, characterization and theoretical calculations of model compounds of silanols catalyzed by TEMPO to elucidate the presence of Si–O–Si and Si–O–N bonds

We report the results from the reactions of 1-phenylethanol, 2-methylpropanol, trimethylsilanol and triphenylsilanol with TEMPO, OH-TEMPO and Br-TEMPO salt at different reaction conditions to obtain model functionalized compounds. With 1-phenylethanol, the ketone compound was obtained as expected, but when using triphenylsilanol the corresponding hexaphenyldisiloxane [di(triphenylsilane)ether] was obtained in crystal form, as well as the silaneoxiamine (Si–O–N). The hexaphenyldisiloxane crystal belonged to the triclinic crystal system with a space group P, a = 8.5829(4) A, b = 9.4856(4) A, c = 10.9694(5) A, α = 95.951(4)°, β = 90.059(3)°, γ = 113.352(4)°, the asymmetric unit comprised of Z = 1. The results showed that the synthetic method to obtain silane ether is simple and can be completed in one step, as well as independently of the type of TEMPO and base used. Also, under the same reactions conditions, we prepared the corresponding TEMPO-containing silanes as triphenylsilaneoxiamine and observed formation of Si-oxide chains through an in situ polycondensation reaction. The resulting compounds were characterized by FT-IR spectroscopy, mass spectrometry (EI), and 1H-NMR. The best assignment for infrared spectroscopy characterization and the structural parameters by vibrational frequencies were determined by DFT calculations.

X-ray molecular structure and theoretical study of 1,4-bis[2-cyano-2-( o -pyridyl)ethenyl]benzene

The structural characterisation of the molecule 1,4-bis[2-cyano-2-(o-pyridyl)ethenyl] benzene obtained through Knoevenagel condensation is reported. The single crystals, as light brown rods, were cultured from a chloroform solution using a slow evaporation method at ambient temperature. The compound crystallised in the monoclinic system belonging to the C2/c space group with a = 26.4556(9) Å, b = 3.73562(10) Å, c = 18.4230(6) Å, β = 109.841(4)° and the asymmetric unit comprising Z = 4. The structure is ordered and the molecules of the title compound exhibited a lattice with water molecules located at sites of inversion and two-fold axial symmetries. Thus, only halves of the molecules are symmetrically independent. The lattice is reported and contrasted with X-ray single-crystal diffraction and theoretical calculations of 1,4-bis(1-cyano-2-phenylethenyl)benzene. By using density functional theory (DFT) and second order Moller-Plesset (MP2) theoretical calculations, the ground state geometry in the whole molecule at the B3LYP/6-31+G(d,p), and MP2/6-31+G(d,p) theory levels, respectively, were optimised. The DFT calculations showed a quasi-planar structure of the molecule, whereas the wave function-based MP2 method afforded a non-planar optimised structure with significant torsion angles between the pyridine and phenyl rings.

X-ray Structures of Precursors of Styrylpyridine-Derivatives Used to Obtain 4-((E)-2-(Pyridin-2-yl)vinyl)benzamido-TEMPO: Synthesis and Characterization

The synthesis and characterization of the precursor isomers trans-4-(2-(pyridin-2-yl)vinylbenzaldehyde (I), trans-4-(2-(pyridin-4-yl)vinylbenzaldehyde (II), trans-4-(2-(pyridin-2-yl)vinylbenzoic acid (III) and (E)-4-(2-(pydridin-4-yl)vinylbenzoic acid (IV) are reported. These compounds were prepared in order to obtain trans-4-((E)-2-(pyridin-2-yl)vinyl)benzamide-TEMPO (V). Compounds I and II were obtained by using a Knoevenagel reaction in the absence of a condensing agent and solvent. Oxidation of the aldehyde group using the Jones reagent afforded the corresponding acid forms III and IV. A condensation reaction with 4-amino-TEMPO using oxalyl chloride/DMF/CH2Cl2 provided the 4-((E)-2-(pyridin-2-yl)vinyl)benzamide-TEMPO. Single crystals of compounds I, II and III were obtained and characterized by X-ray diffraction. Compound I belongs to space group P21/c, a = 12.6674(19) Å, b = 7.2173(11) Å, c = 11.5877(14) Å, β = 97.203(13)° and the asymmetric unit was Z = 4, whereas compound II was in the space group P21, with a = 3.85728(9) Å, b = 10.62375(19) Å, c = 12.8625(2) Å, β = 91.722 (2)° and the asymmetric unit was Z = 2. Compound III crystallized as single colorless needle crystals, belonging to the monoclinic system with space group P21, with Z = 2, with a = 3.89359(7) Å, b = 17.7014(3) Å, c = 8.04530(12) Å, β = 94.4030 (16)°. All compounds were completely characterized by IR, 1H-NMR, EI-MS and UV-Vis.

Quantitative analysis of weak non-covalent interactions in (Z)-3-(4-halophenyl)-2-(pyridin-2/3/4-yl)acrylonitriles

A detailed experimental and theoretical investigation on the intermolecular interactions in (Z)-3-(4-halophenyl)-2-(pyridin-2/3/4-yl)acrylonitriles is reported. The intermolecular interactions are analyzed and quantified by PIXEL, DFT and quantum theory of atoms in molecules (QTAIM) calculations. The results showed that the absence of strong classical hydrogen bonds and the presence of several weak intermolecular C–H⋯N, C–H⋯halogen, halogen⋯halogen and π stacking interactions play important roles in the stabilization of crystal structures. Four different π stacking dimers (homo parallel, homo slipped parallel, hetero anti-parallel and hetero anti-parallel slipped) are observed and found to be the most stabilized dimeric motifs in all structures. The hetero anti-parallel (−10.6 kcal mol−1) and slipped anti-parallel (−9.1 kcal mol−1) π⋯π interactions have the highest stabilization energies among the other interactions observed in the present study. The substituted halogen atoms (X = F, Cl and Br) are involved in the variant and invariant C–H⋯X, C⋯X and halogen⋯halogen interactions in all three families. The relative contributions of various non-covalent interactions are calculated using Hirshfeld surface analysis and 2D fingerprint plots. Further, detailed UV-vis spectral studies are reported for the title compounds in solution and solid phases. These results are compared with the simulated spectra and good agreement is found between experimental and theoretical spectra.