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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]

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]

8-hydroxyquinoline is a plant natural compound, but it can be also obtained by synthesis, with a wide range of applications. An extensive theoretical investigation of 8-hydroxyquinoline, performed by quantum-mechanical modeling, give important information on the physical properties of this molecule. A solvatochromic study of 8-hydroxyquinoline was also performed, the results of which allowed to estimate the contribution of each type of intermolecular interactions to the total spectral shift of the absorption band. Also, the electric dipole moment in the excited state of this molecule was estimated by the variational method and by Abe's model. [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]

Abstract The zwitterionic molecule Benzo-[f]-Quinolinium Acetyl Benzoyl Methylid (BQABM) is studied in this paper from quantum mechanical and solvatochromic point of view. The nature and contribution of each type of intermolecular interaction to the spectral shifts in different solvents were estimated based on solvatochromic analyze of BQABM visible absorption band. The correlation coefficients for the dependence of the wavenumber in the maximum of BQABM visible band vs. the solvent parameters were computed by Linear Energy Relationships Simulation (LERS). The optimized geometry of BQABM and some physical and chemical parameters for isolated molecule in its ground electronic state were obtained with Spartan'14 programs. The results obtained in quantum mechanical analysis and also LERS correlation coefficients were used to determine the excited state dipole moment of BQABM by a Variational method in McRae and Kawschi hypothesis that the molecular polarizability does not change in the visible absorption process. An increase in the BQABM electric dipole moment by excitation resulted in our study. Graphical Abstract Unlabelled Image Highlights • BQABM is a zwitterionic compound with a visible charge transfer band. • Estimation of interaction strength in each solvent • Excited state dipole moment of BQABM • Angle between the dipole moments in electronic states of visible absorption process [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]