Dana Ortansa Dorohoi

Brilliant blue G is a chemical compound with many important applications in various domains, from dye manufacturing to biotechnologies and medicine. Despite the fact that it is used mainly in solutions, a solvatochromic study of this compound has never been reported, while the value of the electrical dipole moment in the excited state is unknown. Here, a solvatochromic study of brilliant blue G is described, and the data is analyzed by three models, allowing for the estimation of the intermolecular interactions involved, as well as their contribution to the total shift in the visible electronic absorption spectral band. Two models provide a predominance of the non-specific (universal) intermolecular interactions, while the third model overestimates the weight of the specific interactions. The spectral data also allow for the comparative estimation of the electrical dipole moment in the first excited state of brilliant blue G molecule by two methods. The values obtained are very close, confirming the good agreement between the two approaches. One of these methods also estimates the angle between the electrical dipole moments in the ground and excited states of brilliant blue G molecule, respectively.

Three derivatives of benzo-[f]-quinolinium ylids, which all underwent an intermolecular charge transfer process, were used as solvatochromic indicators to study the specific solvent–solute interactions in binary mixtures of protic–aprotic solvents with different molar ratios. The microenvironment around the solute molecules was observed via electronic absorption spectroscopy and was analyzed by employing solvation models and quantum chemical calculations. The spectral analysis suggested that the solute was preferentially solvated by the polar protic solvent, indicating a lack of synergy between the two solvents. The solvation microsphere was progressively occupied by the protic solvent, on the basis of specific solute–solvent interactions. By modeling the 1:2 (solute-coordinating solvent) complexes with explicit solvents, the binding energy for complex formation was estimated.

Dimazon is known to stimulate the proliferation of epithelial cells. The dimazon released from locally attached polymer foils could be efficient for the treatment of skin damage. So, knowledge on the characteristics of the dimazon released from polymer matrices is important in establishing the continuous and predictable delivery of drug to a target. The spectrum of dimazon released from PVA foils is analysed based on the empirical Korsmeyer–Peppas model. The influence of the drug’s concentration and the film’s anisotropy, induced by stretching, on the delivery mechanism is highlighted. The results of this study could help clinical researchers establish a protocol for using dimazon from PVA foils in skin therapy.

The solvatochromic properties of 48 solvents of three benzo-[f]-quinolinium methylids (BfQs) were analyzed within the theories of the variational model and Abe’s model of the liquid. The electro-optical properties of BfQs in the first excited state were determined based on the charge transfer process that occurs from the ylid carbon to the nitrogen atom. The dipole moments and the polarizabilities in the first excited state were calculated according to the two models. The quantum chemical calculations helped in understanding the relationship between the molecular structure and absorption properties of the ground state. It is concluded that several key parameters modulate the strength of the charge transfer and they work in synergy, and the most important are as follows: (i) isomerism around the single polar bond, and (ii) the properties of the solvent. The link between geometrical conformation and the zwitterionic character make the studied BfQs very sensitive chromophores for sensors and optical switching devices.

Transparent polymers are key materials for producing a broad category of optical components. For specific uses, the material needs additional adaptation of its basic properties. In this context, the current article is focused on applying two kinds of treatments for tailoring the optical and morphological features of low-density polyethylene to match the criteria as optical retardation plates or band-pass filters. The first kind of treatment involves combined mechanical stretching (at various degrees) and abrasion. The second type of treatment resides in polymer foil exposure to plasma and immersion in a solution of a triphenylmethane derivative. For optical compensation purposes, the polymer foils were subjected to combined mechanical treatments consisting of stretching (at various degrees) and abrasion. To assess the level of produced molecular ordering, the polyethylene films were subjected to polarized infrared spectral measurements, polarized refractometry tests and morphological analyses by polarized light microscopy and atomic force microscopy. The results indicated that inducing birefringence and morphology anisotropy of samples leads to proper optical retardation. For optical filter purposes, the dyed polymer was shown to have changes in colorimetric parameters and morphological features and absorbed radiation in the interval of 480–660 nm, while others were transmitted. These characteristics are adequate for band-pass filter uses.

Binary solvent mixtures of the non-ionic surfactant Triton X-100 with water, methanol, ethanol, and 1-propanol, respectively, were investigated by solvatochromic studies. The absorption spectral bands of methyl red dye, used as a solvatochromic probe, were recorded in ternary solutions prepared with different mole ratios between Triton X-100 and water/alcohols. The Kamlet–Abboud–Taft model was applied to estimate the contribution of each type of intermolecular interaction to the total shift of the electronic absorption band of the solute. The composition of the solute molecule’s first solvation shell was comparatively estimated by using three models: the statistical cell model of ternary solutions, the Suppan model, and the Bosch–Rosés model. The statistical cell model allows the estimation of the difference between the interaction energies in the solute–solvent pairs of molecules. The Bosch–Rosés model provided important information on the 1:1 complex formed between Triton X-100 and water/alcohol molecules, as well as on the symmetry/asymmetry related to the binary mixtures in the cybotactic region of the solute’s molecule.

A rapid and simple spectral method for determining the linear birefringence of thin anisotropic films, using the channeled spectra, is proposed in this article. Two channeled spectra must be recorded for a transparent system containing a thick anisotropic layer and a thin stretched polymer film, when the two anisotropic uniaxial layers have parallel and perpendicular optical axes, respectively. The sum and difference of the two channeled spectra indicate (by the positions of the maxima and minima in the resulting channeled spectra) the phase difference introduced by the thin polymer film. One must measure with precision only the thickness of the polymer film in order to compute the linear birefringence of the thin polymer film, using the position of the maxima and minima of the sum and difference. The experimental data obtained for poly (vinyl alcohol)—PVA—and poly (ethylene terephthalate)—PET—films attest to the applicability of the proposed method to the uniaxial transparent polymeric thin films.

Two charge transfer compounds based on pyridazinium ylids were studied by electronic absorption spectroscopy in binary and ternary solutions, with the purpose of evaluating their descriptors of the first singlet excited state and to estimate the strength of the intermolecular interactions in protic solvents. The molecular descriptors of the excited state were comparatively estimated using the variational method and the Abe model of diluted binary solutions. Analysis of electronic properties using density functional theory was performed for several key solvents, in order to understand the solvatochromic behavior. The DFT calculations revealed that, in the polar and strongly interacting solvents, the carbanion and the terminal group become a stronger electron acceptor. The bathochromic shift of the ICT band was confirmed using DFT calculus. The ability of the two ylids to recognize and discriminate the solvents was analyzed with principal component analysis and with cluster analysis. Although the study was performed in 24 solvents, the results showed that the ylids were most sensitive to alcohols, so they can be a useful tool to identify and classify different types of low-alcoholic solvents.

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.

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.