Effects of donor-acceptor groups on the structural and electronic properties of 4-(methoxymethyl)-6-methyl-5-nitro-2-oxo-1,2-dihydropyridine-3-carbonitrile

Synthesis and photochromic properties of some N-phthalimide azo-azomethine dyes. A DFT quantum mechanical calculations on imine-enamine tautomerism and trans-cis photoisomerization

This paper presents synthesis, photophysical characterization and quantum mechanical calculations of some N-phthalimide azo-azomethine dyes. The dyes were synthesized via azo coupling reaction between 2,4-substituted aromatic anilines and salicylic aldehyde followed by condensation reactions between azo dyes and N-aminophtalimide. Quantum chemical calculations to optimise the molecular geometry and to determine the electron densities of the trans (E) imine ⇌ enamine and the cis (Z) imine ⇌ enamine isomers and their vibrational frequencies have been computed by using DFT at B3LYP/6-31 + G(d,p) level of theory in vacuo. The effect of the used DMF solvent on the molecular structure and bond energies has been determined by using the IEFPCM model. Thermodynamic parameters such as total electronic energy E(RB3LYP), enthalpy H₂₉₈ (sum of electronic and thermal enthalpies), free Gibbs energy G₂₉₈ (sum of electronic and thermal free Gibbs energies) and dipole moment μ were computed in order to estimate the ΔE, Δμ, ΔH, ΔG and ΔS values. The NBO analysis was performed in order to understand the intramolecular charge transfer and the energy of resonance stabilization. After molecular geometry optimization, the electronic spectra were obtained by TD-DFT calculations at the above mentioned basis set using the IEFPCM model of DMF as a solvent. The solvatochromic effect of the dyes in four solvents with different polarity has been studied by UV-VIS spectroscopy and compared with the theoretically predicted. The coincidence between measured and calculated spectra is satisfactory. The dynamic photoisomerization experiments were performed in DMF under irradiation with UV light at λ = 365 nm (mostly E → Z) and with VIS light at λ = 400-800 nm (mostly Z → E). The spectra were recorded in the spectral region from 300 to 800 nm at identical sample concentrations of the three dyes and illumination times in order to investigate the photodynamical E → Z → E conversion of the NN chromophore group of the dyes as well as the imine ⇌ enamine tautomerization.

Synthesis, structural and spectroscopic evaluations and nonlinear optical properties of 3,5-bis(4-methoxyphenyl)-4,5-dihydro-1H-pyrazole-1-carbothioic O-acid

In this study, we report a combined experimental and theoretical study on 3,5-bis(4-methoxyphenyl)-4,5-dihydro-1H-pyrazole-1-carbothioic O-acid (C18H18N2O3S) molecule. The compound crystallizes in the trigonal space group R-3 with a=b=27.7151(12) Å, c=12.4866(6) Å, α=β=90.0°, γ=120.0° and Z=18. The crystal packing is stabilized by O-H⋯O and O-H⋯S intermolecular hydrogen bonds. These hydrogen bond interactions are also proved by NBO analysis. A detailed spectroscopic investigation is performed by the application of FT-IR and FT-NMR in addition to the theoretical approaches. Small energy gap between the frontier molecular orbitals is responsible for the nonlinear optical activity of the title molecule.

The effects of electronegative substituent atoms on structural, vibrational, electronic and NLO properties of some 4-nitrostilbene derivates

Organic compounds which have one or more aromatic systems in conjugated positions show charge transfer interactions which are responsible for the non-linear properties of the compounds. A conjugated π electron system enables a pathway for the entire length of conjugation under the perturbation of an external electric field. When electron donating and withdrawing moieties are located at terminal position of conjugated backbone, nonlinear optical (NLO) properties have been increased significantly which involve the correlated and high delocalized π electron states. Recently synthesized organic complexes, 1-(4-fluorostyryl)-4-nitrostilbene (1), 4-Chloro 4-nitrostilbene (2), 4-Bromo 4-nitrostilbene (3) and 4-Iodo 4-nitrostilbene (4), were simulated using density functional theory (DFT). Based on the optimized geometries, spectroscopic and NLO properties of these complexes were discussed as compared with each other.