Search

Theoretical bases of the solvent influence on the electronic spectra of binary and ternary solutions of some zwitterionic compounds are discussed. Three cycloimmonium ylids were investigated as spectrally active zwitterionic compounds. The energetic and electro-optical parameters of the studied molecules were obtained by using Spartan´14 programs. Some linear dependences between the wavenumbers in the maxima of the electronic spectra of the studied compounds and the solvent parameters are established. The value of the excited state dipole moment and its orientation relative to the ground state dipole moment are established based on the theories regarding the solvent influence on the electronic absorption spectra. The difference between the interaction energies in molecular pairs: ylid-solvent (1) and ylid-solvent (2) is estimated based on the statistical cell model of ternary solutions. These studies offer information about the composition of the first molecular shell surrounding the spectrally active molecules and about the nature and strength of the interactions between these molecules and their neighboring shell. Most of the ylid reactions take place in situ and from this point of view the knowledge regarding their reactivity and their interactions with solvents are very important. [ABSTRACT FROM AUTHOR]

Four carbanion monosubstituted 4'-aryl-1,2,4-triazol-1-ium-4-R2-phenacylids, used as precursors in obtaining new heterocyclic compounds, and their corresponding derivatives belonging to the C2v point group of symmetry were studied by computational means in dimethylformamide (DMF) solutions compared with their isolated state. The changes in the computed parameters induced by the solvent compared with those of the isolated molecules were analyzed in this paper. The charge distribution and the molecular energies in the HOMO and LUMO, the electronic states responsible for the visible absorption band of 4'-aryl-1,2,4-triazol-1-ium-4-R2-phenacylids, in their isolated state and in solutions achieved in DMF were computed and compared with the visible electronic absorption spectra. The molecular descriptors of the studied compounds were computed, and the higher reactivity of the carbanion monosubstituted 4'-aryl-1,2,4-triazol-1-ium-4-R2-phenacylids compared with symmetric derivatives was established. The obtained results can help researchers to obtain new heterocycles with applications in the drug industry. [ABSTRACT FROM AUTHOR]

Abstract: Compounds with basic character, N-ylids can be involved in specific interactions with protic solvents. Consequently, “long range” (universal) and “short range” (specific) forces act simultaneously in the protic solutions of N-ylids. The contributions of these interactions to the total spectral shift measured in the Electronic Absorption Spectra (EAS) were separated on the basis of solvatochromic effects. Supplemental spectral shifts measured in protic solvents compared with aprotic ones increases with the chemical shift of –OH signal from the 1H Nuclear Magnetic Resonance (NMR) spectra of the protic solvents. Important information about the strength of the specific interactions was obtained from the spectral study of N-ylids ternary solutions in binary solvents with protic and non-protic molecules. The model of ternary solutions was used to estimate the potential energy in the molecular pairs of the type N-ylid-protic solvent. [Copyright &y& Elsevier]

Abstract: The spectral shifts in the visible electronic absorption spectra of three amino-nitro-benzene derivatives in different solvents were correlated with the macroscopic parameters (refractive index and electric permittivity) of the solvents. The wavenumbers in the maximum of the visible charge transfer absorption band of o-nitro-aniline, 4-amino-3-nitrophenol and 3-amino-4-nitrophenol depend linearly on the Baur–Nicol function of electric permittivity. This dependence allows to estimate the electric polarizability in the electronic excited states if the electric polarizability in the ground state of the spectrally active molecule is determined by other procedures, such as by quanto-mechanical calculations. [Copyright &y& Elsevier]

Four carbanion monosubstituted p-aryl-1,2,4-triazol-1-ium methylids are subjected to a comparative study between their spectral and quantum-mechanical parameters in order to obtain more information about their structural features in hydroxyl solvents as water and ethanol and also on the nature of electronic absorption transitions from the visible range. The quantum mechanical analysis, made by the Spartan'14 program, established a series of molecular parameters of the studied ylids important for their reactivity and for intermolecular interactions with hydroxyl liquids. An extensive solvatochromic study of 1,2,4-triazol-1-ium ylids is impossible due to their limited solubility in liquids. Binary solvent mixtures of water and ethanol with known solvent parameters from the literature were used for this study. The electronic absorption spectra in binary solvents water and ethanol were used to establish the influence of intermolecular interactions on the spectral characteristics of the studied methylids and also on the composition of their first solvation shell in ternary solutions. The difference between the interaction energies in molecular pairs ylid–water and ylid–ethanol was determined based on the statistical cell model applied to the ternary solutions of the type of ylid + water + ethanol. The obtained values are very small due to the hydroxylic nature of the two solvents. [ABSTRACT FROM AUTHOR]

Abstract The solvatochromic study of fluorescein is performed in order to obtain information on both the interactions with solvents in which it is dissolved and the electro-optical parameters of the molecule in the first excited electronic state. The shifts of the visible absorption spectral band of fluorescein dissolved in several solvents were experimentally measured and correlated to solvent parameters such as the refractive index, electrical permittivity and the Kamlet-Taft parameters (hydrogen bond acidity and basicity, respectively). A quantum-mechanical study of the fluorescein molecule was additionally performed to determine some parameters of the fluorescein molecule in the ground electronic state. Following McRae's hypothesis, according to which the molecular polarizability does not change in the absorption process, the data obtained from the solvatochromic analysis and quantum-mechanical calculations were corroborated in order to estimate the dipole moment of fluorescein in its first excited electronic state. Highlights • Computational and solvatochromic studies of fluorescein were performed. • Excited states dipole moment of fluorescein molecule was estimated. • Transitions π → π * take place with increase of the molecular dipole moment. [ABSTRACT FROM AUTHOR]

Highlights: [•] The spectral study of some DPH+THF multicomponent solutions in ethanol+water binary solvent has been correlated with the computation results. [•] The frequency shifts in absorption spectra, previously attributed to dispersive forces, depend on the ratio of E/W in binary solvent. [•] The molecular composition of the first solvation shell of DPH in multicomponent solutions essentially depends on the content E/W of the binary solvent. [•] In solutions with high water content, THF forms micelles around the DPH molecules, electronic spectra becoming solvent-independent. [Copyright &y& Elsevier]

Abstract Three azo-derivatives: 2, 2′-Dihydroxyazobenzene (DHAB), Sudan Orange G (SOG) and 4-(Phenylazo) diphenylamine (PDA) were studied in this paper from quantum-mechanical and spectral point of view. The nature and the contribution of the intermolecular interactions to the spectral shifts in the solutions of the studied azo-derivatives were established based on the existent theories. Some electro-optical parameters of the studied molecules were calculated with Spartan 14 software using Density Functional Theory (DFT) employing the B3LYP model and the standard 6-31G* basis set. The polarizability and dipole moment in the excited states were estimated considering the variation of the angle between dipole moments in electronic states giving the visible absorption band. Graphical abstract Unlabelled Image Highlights • Visible absorption bands appear through the same mechanism. • The dispersion interactions are predominant in the studied solutions. • The dipole moment of the studied azo-derivatives increases by excitation. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate the relations between the properties of some organic compounds that are cycloaddition derivatives of benzo[ f ]quinoline, namely benzo[ f ]pyrrolo[1,2- a ]quinolines (BQCDs) and the structure of variable substituent in the addition cycle. The work was focused on the differences in the molecular parameters like frontier orbitals and dipole moment as well as electronic absorption spectra of substituted BQCDs. The optimized molecular structures of BQCDs were calculated using Gaussian 09, with DFT method, the frontier orbitals and electronic absorption spectra being modeled with restricted Hartree Fock method also implemented in Gaussian 09. Influence of substituted radical on the dipole moments and frontier orbital energies of the BQCDs was evidenced from calculated values. Substituent effect on the BQCDs recorded electronic absorption spectra in diluted solution and protonated diluted solution was also emphasized: different types of the transitions underlying absorption bands in the visible range were presumed based on the quantum chemical and experimental investigation. [ABSTRACT FROM AUTHOR]