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The electronic absorption spectral characteristics of cycloimmonium ylids with a zwitterionic structure have been analyzed in forty-three solvents with different hydrogen bonding abilities. The two ylids lack fluorescence emission but are very dynamic in electronic absorption spectra. Using the maximum of the ICT band, the goal was to establish an accurate relationship between the shift of the ICT visible band and the solvent parameters and to estimate two of the descriptors of the first (the) excited state: the dipole moment and the polarizability. Two procedures were involved: the variational method and the relationships of the Abe model. The results indicate that the excited state dipole moment of the two methylids decreases in the absorption process in comparison with the ground state. The introduction of a correction term in the Abe model that neglects the intermolecular H-bonding interactions leads to a more accurate determination of the two descriptors. The strong solvatochromic response of both ylids has been further applied in distinguishing the solvents as a function of their specific parameters. Principal component analysis was applied to five selected properties, including the maximum of the charge transfer band. The results were further applied to discriminate several binary solvent mixtures. [ABSTRACT FROM AUTHOR]

Fluorescein sodium is a very important compound for a wide spectrum of applications, from which medical applications prevail. Despite this, there are very few studies in the literature related to the structure and fundamental properties of fluorescein sodium and its solutions, with most of the studies dealing with fluorescein. The purpose of the present article is to determine some parameters of the fluorescein sodium molecule approaching the quantum-mechanical modeling and experimental solvatochromism in both binary and ternary solutions. For data analysis, several theoretical models were applied. The results highlight the intermolecular interactions involved in the spectral shift of the electronic absorption band of fluorescein sodium when dissolved in different solvents or binary solvents and allowed the estimation of the difference between the interaction energy in molecular pairs of the type of fluorescein sodium − solvent 1 and fluorescein sodium − solvent 2. By applying a variational method, the dipole moment in the first excited state of the fluorescein sodium molecule and the angle between the dipole moments in the ground and excited states, respectively, were estimated. These results are useful for a better understanding of the behavior of fluorescein sodium when dissolved in different solvents or combinations of solvents, to develop new practical applications. [ABSTRACT FROM AUTHOR]

The nature and strength of the molecular interactions were established by solvatochromic studies of 22 binary and 42 ternary diluted solutions of pyridinium–carbethoxy–anilidomethylid (PCAnM). The visible absorption band of PCAnM, due to an intramolecular charge transfer (ICT) from the carbanion towards the heterocycle, shows a great sensitivity to the solvent nature. The spectral data are analysed by linear energy relationship (LERS) and the contribution of each type of interaction to the total spectral shift is estimated. The results from the solvatochromic study and those obtained by quantum mechanical computations were correlated in order to estimate the excited state dipole moment of the studied methylid. The decrease of the dipole moment by excitation emphasized in this study corresponds to the ICT nature of the visible absorption band of the solute. The ternary solutions of PCAnM achieved in mixtures of water with primary alcohols (ethanol and methanol) show the dependence of the visible band on the molar fraction of water and give the difference between the interaction energies in molecular pairs of the type water–methylid and alcohol–methylid, computed based on the statistical cell model of ternary solutions. The decrease in strength of the hydrogen bond between PCAnM and the protic solvent molecules was estimated in the following order: water > methanol > ethanol. The results from this study can be utilized in Organic Chemistry to generate knowledge of the interactions with solvents when cycloimmonium methylids are used as precursors to obtain new heterocycles and also in Quantum Chemistry to obtain a better description of their excited electronic states. [ABSTRACT FROM AUTHOR]

The 1-dithiocarboxy-2-ethoxy-1-(isoquinolin-2-yl)-2-oxoethan-1-ylid (iQTCY) zwitterionic molecule has been studied by computational and spectral means in order to establish some of its structural parameters in the ground electronic state as well as the nature and the strength of its universal and specific interactions with different solvents. The prevalence of the orientation–induction interactions in the diluted solutions of iQTCY in aprotic solvents and the additional specific interactions by hydrogen bonds (HB) in the protic solvents were demonstrated. Three theoretical models were comparatively used to estimate the composition of the first solvation shell of the iQTCY molecule in ternary solutions. The difference between the interaction energies in molecular pairs solute–solvent was computed based on the statistical cell model of ternary solutions of iQTCY in mixtures of water–ethanol and water–methanol. Using the electro-optical parameters computed by the quantum-mechanical technique and the results of the solvatochromic study, the excited state dipole moment of iQTCY was estimated within the limit of the variational method applicable to molecules that show only an absorption electronic spectrum. [ABSTRACT FROM AUTHOR]

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]

Quantum mechanical analysis using Spartan'14 was combined with solvatochromic study of binary and ternary solutions of some azo-derivatives. Correlation between the electro-optical molecular parameters established by computation and the wavenumbers in the maximum of the visible electronic absorption band of the studied azo-derivatives were established. The excited state dipole moment and the angle between the dipole moments in the electronic states participating in the absorption process were estimated based on the theory of the solvent influence on the electronic spectra. The variational method was used for estimating the molecular parameters in the excited state of the studied molecules. [ABSTRACT FROM AUTHOR]

Two pyridazinium-p-nitro-phenacylids with different structure of heterocycle are studied in this paper from quantum-mechanic and spectral point of view. The dipole moment and the polarizability of ylids in their ground electronic state estimated by HyperChem and the regression coefficients established in solvatochromic analysis are used to compute the excited state dipole moment of each ylid and the angle between the dipole moments in the ylid electronic states participating to the absorption process. [ABSTRACT FROM AUTHOR]

Quercetin was subjected to a quantum-mechanical analysis and energetic and electro-optic parameters were evaluated. A solvatochromic study was used to estimate the dipole moment of quercetin in the excited state and to determine the angle between the dipole moments of this molecule in the electronic states responsible for the visible absorption band. The contribution of each type of intermolecular interactions to the total spectral shift experimentally recorded in quercetin solution was also established in this study. [ABSTRACT FROM PUBLISHER]

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]

Abstract: The electric dipole moments involved in the electronic transitions were determined by using theories about the solvent influence on the wavenumbers in the maximum of the electronic bands. The contributions of the intermolecular interactions upon the spectral shifts as function of the solvent macroscopic parameters (electric permittivity and refractive index) were expressed by multiparameter regressions. The obtained regression coefficients were used to determine the dipole moments in the excited states as well as those of the electronic transition of some spectrally active molecules, such as anthracene derivatives, cycloaducts of benzo-[f]-quinolinium, 4-amino-phthalimide and p-phenyl-pyridazinium-dibenzoyl methylid. The polarizabilities in the excited states were estimated on the basis of Abe''s theory [1]. The anthracene derivatives and cycloaducts of benzo-[f]-quinolinium were considered for this study, because the underlying theory applies for liquids with non-polar molecules. For the polar molecules, 4-amino-phthalimide and p-phenyl-pyridazinium-dibenzoyl methylid, Bakhshiev''s theory was applied. The values of the dipole moments and polarizabilities obtained by using different models are discussed taking into consideration the limitations of the theories, which express the spectral shifts as functions of the solvent macroscopic parameters, and of the electro-optical parameters of the studied molecules. [Copyright &y& Elsevier]

The results obtained in molecular modeling achieved for some carbanion mono-substituted and di-substituted 1(N)-[(para-R2)-phenacyl]–4(N)-[(para-R1)-phenyl]-1,2,4-triazolium-methylides and the information from the NMR, IR, and UV-VIS spectra were used to do a qualitative estimation of the stability and the reactivity of these compounds. The molecular electric dipole moments were theoretically and experimentally estimated. [ABSTRACT FROM AUTHOR]

The results obtained both in quantum chemical computation and in solvatochromic study of pyridinium di-carbethoxy methylid (PCCM) are correlated in order to estimate the electric dipole moment in the excited state of this molecule. This estimation is made by a variational method in the hypothesis that the molecular polarizability does not change in time of the absorption process. Ternary solutions of PCCM in protic binary solvents are used here, both establishing the contribution of each type of interaction to the spectral shift and to characterize the composition of the first solvation shell of PCCM. Results are compared with those obtained before for other binary solvents. The difference between the interaction energies in molecular pairs of PCCM-active solvent and PCCM-less active solvent was also estimated based on the cell statistical model of the ternary solutions. [ABSTRACT FROM AUTHOR]

Electronic absorption and fluorescence spectra of two Rhodamine dyes (Rhodamine B and Rhodamine 6G) in binary solutions are studied in this paper. The excited state dipole moments have been computed using the correlation coefficients obtained by linear solvation energy relationship (LSER) applied to electronic spectra and the values of the dipole moments in the ground state of Rhodamines computed by HyperChem 8.0.6. The nature and the contributions of each type of interactions to the spectral shifts from visible range are established based on solvatochromic analysis. [ABSTRACT FROM AUTHOR]