Solvent Polarity Scale Research Articles

The Influence of the Alkylamino Group on the Solvatochromic Behavior of 5-(4-substituted-arylidene)-1,3-dimethylpyrimidine-2,4,6-triones: Synthesis, Spectroscopic and Computational Studies.

Advances in electronics and medical diagnostics have made organic dyes extremely popular as key functional materials. From a practical viewpoint, it is necessary to assess the spectroscopic and physicochemical properties of newly designed dyes. In this context, the condensation of 1,3-dimethylbarbituric acid with electron-rich alkylaminobenzaldehyde derivatives has been described, resulting in a series of merocyanine-type dyes. These dyes exhibit intense blue-light absorption but weak fluorescence. An electron-donating alkylamino group at position C4 is responsible for the solvatochromic behavior of the dyes since the lone electron pair of the nitrogen atom is variably delocalized toward the barbituric ring, which exhibits electron-withdrawing properties. This was elucidated, taking into account the different geometry of the amino group. The intramolecular charge transfer in the molecules is responsible for the relatively high redshift in absorption and fluorescence spectra. Additionally, an increase in solvent polarity moves the absorption and fluorescence to lower energy regions. The observed solvatochromism is discussed in terms of the four-parameter Catalán solvent polarity scale. The differences in the behavior of the dyes were quantified with the aid of time-dependent density functional theory calculations. The obtained results made it possible to find regularities linking the basic spectroscopic properties of the compounds with their chemical structure. This is important in the targeted search for new, practically important dyes.

The Preferential Solvation of Methyl Red in Various Binary Aqueous Solutions: Solvatochromism, Preferential Solvation Parameters, Microheterogeneity of Solvents and Polarity Scale.

The solvatochromic characteristics of methyl red were examined in several aqueous solutions from pure water, with methanol, ethanol, propanol, acetonitrile, and dioxane. In order to explain the preferred solvation of the probe azo dye in the binary mixed solvents, the solvent exchange model of Bosch and Roses was used to evaluate the association between the empirical solvent polarity scale (ET) values of MR and solvent composition. Non-linear solvatochromism of methyl red was noted in all aqueous mixtures containing methanol, ethanol, propanol, acetonitrile, and dioxane. In addition to calculating the local mole fraction of each solvent composition in the cybotactic area of the probe, the impact of the solvating shell composition on the preferential solvation of the solute dye was examined in terms of both solvent-solvent and solute-solvent interactions. The local mole fraction of each solvent composition in the cybotactic region of the probe was also calculated. The results indicated that the MR solvation shell was thoroughly saturated with the solvent complex S12 in the following order: dioxane > ethanol > methanol > acetonitrile > propanol. Data from the binary systems were analyzed with KAT parameters using a multi-model; in aqueous methanol and ethanol solutions, the hydrogen acidity was more responsible for the spectral shift, whereas in aqueous acetonitrile and dioxane solutions, the basicity has a greater influence.

Strongly fluorescent indolizine-based coumarin analogs

Blue to yellow-emitting 2-oxo-pyrano[2,3-b]indolizines, which are efficiently prepared in two steps from pyridinium salts, have strong emission across the solvent polarity scale.

The non-ideality in binary aqueous systems contributed to the different abilities of solvent entities incorporated in the solvation shell of methylene blue

The solvatochromic properties of methylene blue (MB) were investigated in neat water, methanol, ethanol, propanol, dioxane and their corresponding aqueous mixtures. The correlation of the empirical solvent polarity scale (ET) values of MB with solvent composition was analysed using the solvent exchange model of Bosch and Roses to explain the preferential solvation of the probe thiazine dye in the binary mixed solvents. Non-linear solvatochromism of MB was observed in aqueous mixtures of methanol, ethanol, propanol and dioxane. The influence of the composition of the solvating shell in preferential solvation of the solute dye was investigated in terms of both solvent?solvent and solute?solvent interactions, and the local mole fraction of each solvent composition in the cybotactic region of the probe was also calculated. Effective mole fraction variation can provide important physicochemical insights into the microscopic and molecular interactions between MB species and solvent components. The results showed that the MB solvation shell was thoroughly saturated with the solvent complex S12 for dioxane more than ethanol and propanol mixtures, and opposite trends for methanol mixtures, whereas the solvent complex S12 could not incorporate into the MB solvation shell. Data from the binary systems were analysed with KAT parameters using a dual model of basicity and polarity. The results showed that the polarity was better suited for spectral shift in aqueous methanol and ethanol solutions, while the basicity was better for aqueous propanol and dioxane solutions.

Fluorescence based studies on the interaction and characterization of surface-active ionic liquids with polarity sensitive intramolecular charge transfer probe

Surface-active ionic liquids (SAILs) are of tremendous interest in recent times due to their improved application in the field of food, detergent, and health. The modulated fluorescence behavior of an intramolecular charge transfer (ICT) probe, trans‐ethyl‐p‐(dimethylamino) cinnamate (EDAC), in presence of five different SAILs with varying head groups (viz. imidazolium, pyridinium, and morpholinium) and different alkyl chain length (decyl, dodecyl, and tetradecyl) was monitored by steady state and time-resolved fluorescence spectroscopy. Extreme sensitivity of EDAC fluorescence was used to characterize different physicochemical properties of the SAILs, including critical micelle concentration, static polarity, and empirical solvent polarity scale, ET(30) of the microenvironment. The estimated parameters are in good agreement with the literature reports and measured independently from other complimentary experiments discussed here. Time‐resolved fluorescence experiments show a significant retardation in different nonradiative decay channels of EDAC, when compared to that in aqueous phase, indicating a preferential association of the probe in presence of SAILs. The results indicate that the physicochemical properties of SAILs can be tuned by controlling the nature of both the cations and as well as the chain length of the alkyl group. These properties also show significant modulation in solutions with varying SAIL concentration, particularly in the pre- and post-micellar region. The results, particularly the surface-active properties and the self-assembly behavior presented in this study, are expected to provide new knowledge towards the design and development of novel SAILs with specific industrial and biological applications.

Reichardt’s Dye-Based Solvent Polarity and Abraham Solvent Parameters: Examining Correlations and Predictive Modeling

The concept of “solvent polarity” is widely used to explain the effects of using different solvents in various scientific applications. However, a consensus regarding its definition and quantitative measure is still lacking, hindering progress in solvent-based research. This study hopes to add to the conversation by presenting the development of two linear regression models for solvent polarity, based on Reichardt’s ET(30) solvent polarity scale, using Abraham solvent parameters and a transformer-based model for predicting solvent polarity directly from molecular structure. The first linear model incorporates the standard Abraham solvent descriptors s, a, b, and the extended model ionic descriptors j+ and j−, achieving impressive test-set statistics of R2 = 0.940 (coefficient of determination), MAE = 0.037 (mean absolute error), and RMSE = 0.050 (Root-Mean-Square Error). The second model, covering a more extensive chemical space but only using the descriptors s, a, and b, achieves test-set statistics of R2 = 0.842, MAE = 0.085, and RMSE = 0.104. The transformer-based model, applicable to any solvent with an associated SMILES string, achieves test-set statistics of R2 = 0.824, MAE = 0.066, and RMSE = 0.095. Our findings highlight the significance of Abraham solvent parameters, especially the dipolarity/polarizability, hydrogen-bond acidity/basicity, and ionic descriptors, in predicting solvent polarity. These models offer valuable insights for researchers interested in Reichardt’s ET(30) solvent polarity parameter and solvent polarity in general.

Effect of Solvent Polarity on the Spectral Characteristics of 5,10,15,20-Tetrakis(p-hydroxyphenyl)porphyrin.

The electronic absorption and vibrational spectra of deprotonated 5,10,15,20-tetrakis(p-hydroxyphenyl)porphyrin (THPP) are studied as a function of solvent polarity in H2O-DMF, H2O-acetone, H2O-methanol, and DMF-acetone mixtures. The maximum absorption wavelength (λmax) of the lowest energy electronic absorption band of deprotonated THPP shows an unusual solvatochromism-a bathochromic followed by a hypsochromic shift with reduced polarity. According to the correlation analysis, both specific interactions (H-bonds) and nonspecific interactions affect the spectral changes of this porphyrin. Furthermore, the solvent polarity scale ET(30) can explain both shifts very well. At higher polarity (ET(30) > 48), THPP exists as a hyperporphyrin. The ET(30) is linear with λmax and a decrease in solvent polarity is accompanied by a bathochromic shift of λmax. These results can be rationalized in terms of the cooperative effects of H-bonds and nonspecific interactions on the spectra of hyperporphyrin. At relatively low polarity (45.5 < ET(30) < 48), hyperporphyrin gradually becomes Na2P as ET(30) reaches the critical value of 45.5. The spectrum of the hyperporphyrin turns into the three-band spectrum of the metalloporphyrin, which is accompanied by a hypsochromic shift of λmax.

Synthesis, Solvatochromism and Estimation of Ground and Excited State Dipole Moments of Silylated Benzothiazole Dyes.

Dyes derived from benzothiazoles are an important class of heterocycles which have remarkable photophysical properties. New photoluminescent 2-phenylbenzothiazole derivatives containing different functional groups were synthesized in high yields and used for silylated derivatives synthesis. The new photoactive compounds were fully characterized and their photophysical properties were investigated. The absorption and fluorescence spectra of the benzothiazoles and their silylated derivatives were evaluated in a series of organic solvents. The results showed that the benzothiazoles present absorption in the ultraviolet range and emission in the blue region with moderate quantum yields and large Stokes shift. The solvatochromism of these compounds was investigated by using Lippert and ET(30) Dimroth-Reichardt empirical solvent polarity scales. The dipole moments obtained by Bakshiev and Kawaski-Chamma-Viallet equations revealed that the excited states were more polar than the ground states.

SOLVATOCROMISMO E AS ESCALAS EMPÍRICAS DE POLARIDADE DO SOLVENTE: UMA REVISÃO

SOLVATOCHROMISM AND THE EMPIRICAL SCALES OF SOLVENT POLARITY: A REVIEW. The term solvatochromism is used to describe the changes in the optical properties of a dye molecule by influence of the solvent characteristics. Solvatochromic shifts are governed by intermolecular interactions between solute-solvent that can be either electrostatic (non-specific interactions) or chemical (specific interactions). Due to the complexity of these interactions and absence of theoretical models that can explain the specific effects of solvent, different authors have introduced empirical parameters to building more reliable solvent polarity scales. Out of various polarity scales that have arisen from this need, those based on the effect of solvent polarity on the electronic excitation energy of indicator organic dyes are the most prevalent in literature. The use of empirical equations that correlate bathochromic (positive solvatochromism) and hypsochromic (negative solvatochromism) shifts of optical spectra of organic molecules with the polarity of solvent has become essential for understanding solute-solvent interactions. This review article presents main mathematical equations that use linear correlations between macroscopic and/or microscopic polarity functions of solvent with spectroscopic parameters of solute (dye) in construction of solvent polarity scales. In addition, main mathematical models that use solvatochromic shifts to estimate the dipole moment of ground and excited state are discussed.

Spectral characteristics of 3,5-diaminobenzoic acid in pure and mixed solvents: Experimental and theoretical study

The effect of solvents on the absorption and fluorescence (FL) spectra of 3,5-diaminobenzoic acid (DABA) was explored in pure solvents of diverse polarities and hydrogen bonding abilities. A bathochromic shift was observed in FL spectra while moving from non-polar to polar aprotic/protic solvents. The solvatochromic-based approaches showed that the dipole moment of DABA in the excited state (ES) is higher than its ground state (GS), which signifies that the ES is more polarized, corresponding to the GS. Moreover, the Catalan solvent polarity scale analysis suggested that the solvent acidity (SA) and dipolarity (SdP) influenced the absorption and FL spectra of DABA in solvents, signifying the presence of non-specific and specific interactions. The FL decay analysis in solvents was correlated with the observed steady-state results and suggested the presence of intramolecular charge transfer (ICT). The preferential solvation concept was utilized to understand the spectral variations of DABA in MeOH-water and DMSO-water mixtures. Further, the computational calculations utilizing the DFT (density functional theory) and TD-DFT (its time extension) for DABA were performed in the gas phase and solvents to estimate the electronic transitions and dipole moments. Furthermore, the natural bond orbital analysis and non-linear optical parameters were also obtained by DFT, and the findings revealed that ICT stabilizes the molecular system. Thus, DABA may have potential applications in the field of optoelectronics and fluorescence sensing.

Application of Reichardt’s Solvent Polarity Scale (ET(30)) in the Selection of Bonding Agents for Composite Solid Rocket Propellants

Bonding agents (BA) are key compounding ingredients for the correct formulation of composite solid rocket propellants (CSRP). In particular, the addition of BA is essential to achieve suitable mechanical properties of CSRP in terms of adequate tensile strength and elongation at the break. It is shown that the polarity of each conventional BA as well as new potential BA can be measured through the Reichardt’s ET(30) polarity scale. Using this methodology, it was possible to propose a substitute for MAPO (tris-(methylaziridinyl)-phosphine oxide), a conventional BA with the drawback of high toxicity and high reactivity, with TTPT (tris-(pyrrolidine)-phosphine oxide), a completely safe and effective BA. In this work, several other potential BA were evaluated through the Reichardt’s ET(30) polarity scale but only a selection of the potential BA were effectively tested in a standard CSRP. The evaluation of TTPT vs. MAPO showing the ability of the former BA to match the mechanical properties of the latter BA was particularly interesting. A reasonable correlation between the elongation at break of the CSRP and the ET(30) value of the BA used in the compound was found.

Synthesis, solvatochromism and DFT study of pyridine substituted benzanthrone with ICT characteristics

We have explored the relation between the substituent and optical nonlinearity of pyridinepiperazine substituted benzanthrone dye. We report the synthesis of 3-(4-(pyridine-2-yl)piperazin-1-yl)-7H-benzo[de]anthracen-7-one (Pyridine-PBA). The molecular structure of the title dye was further confirmed by using FT-IR, 1H NMR, 13C NMR, and X-ray crystallographic techniques. The 3-substituted benzanthrone dye was examined for solvent dependent photophysical properties. The polarity plots indicate that hydrogen bonding interactions are influential in most of the solvents. Further analysis of Stokes’ shift data with multi parameter solvent polarity scale signifies that with an increase in solvent hydrogen bond donor ability a bathochromic shift is observed resulting in an increment in the dipole moment of the Pyridine-PBA dye on excitation. Computational results indicate that the electron excitation has some charge transfer characteristics. Furthermore, the calculated first static hyperpolarizability (β) and second hyperpolarizability (γ) values using range separated DFT methods fare better than the estimates for urea.

Push-pull dyes based on Michler's aldehyde: Design and characterization of the optical and electrochemical properties

Fifteen dyes based on Michler's aldehyde used as the electron donating group and differing by the electron accepting groups have been designed and synthesized. Interestingly, all dyes showed a broad absorption extending over the visible range. Examination of the solvatochromism in twenty-three solvents of different polarities revealed these dyes to give remarkable linear correlations using the Kamlet-Taft solvent polarity scale or the SPP Catalan empirical scales. The different dyes were also characterized by photoluminescence spectroscopy as well as cyclic voltammetry. To get a deeper insight into the optical properties of the different dyes, theoretical calculations were also carried out.

Solvent Effects in Supramolecular Chemistry: Linear Free Energy Relationships for Common Intermolecular Interactions.

The proper choice of solvent is of major importance for all studies in supramolecular chemistry, including molecular recognition in host-guest systems, intramolecular folding, self-assembly, and supramolecular polymerization. In this Perspective, the usefulness of linear free energy relationships (LFERs) is highlighted to unravel the effect of solvents on coordinate bonding (e.g., cation-crown ether), hydrogen bonding, halogen bonding, dipolar aggregation, and π-π-stacking. For all of these intermolecular interactions widely applied in supramolecular systems, LFER relationships between the Gibbs binding energies and common solvent polarity scales including ET(30), π*, α or β based on solvatochromic dyes, scales derived from binding processes such as Gutmann donor and acceptor numbers or hydrogen bond donor and acceptor scales, or physical functions like the Kirkwood-Onsager or the Liptay-Onsager functions could be demonstrated. These relationships can now be applied toward a better understanding of the prevailing intermolecular forces for supramolecular interactions. They further enable a rational selection of the most suitable solvent for the preparation of self-assembled materials and the estimation of binding constants without the need for time-consuming comprehensive investigations of solvents.

The Impacts of Various Media on the Electronic Spectrum of Aniline Violet

The solvent impact can be decided by Solvent polarity scales, a solvatochromic parameter that has a distinctive position of UV-Visible absorption band within the extend between 250 and 700 nm. The spectral characteristics of Aniline Violet in several solvents at room temperature were analyzed which is that the point of considering the impact of solvents on the absorption spectra of this cationic dye in organic solvent of distinctive characters. The solvent impacts on the wavenumber of the absorption band maxima (max) were talked about utilizing the taking after solvent parameters, refractive index, n, relative permittivity, ε and therefore the empirical solvent polarity ET (30), (*,  and ) and (SA, SB, SP and SPd). The solute–solvent interactions were decided on the premise of multilinear solvation energy relationships concept. The fitting coefficients gotten from this analysis allowed us to estimate the contribution of each type of interactions to the total spectral shifts in solution. The set up dependences between max and the solvent parameters emphasize that the visible band of the examined molecule is influenced by both non-specific and specific solute–solvent interactions. The results appeared the solvent polarizability has major impact on the spectral shift instead of hydrogen bonding accepting ability. Catalan strategy show higher acceptable correlation than Kamlet-Taft methodology and Katritzky methodology. The dissociation constant pKa and the isosbestic point of the explored compound were shown the presence of the individual predominate ionic species was assigned by constructing distribution charts at diverse pH ranges. The results showed that the relative permittivity constant, ε, is important factor affecting on the magnitude of the dissociation constant beside the hydrogen bonding of the solvent.

Dyes with tunable absorption properties from the visible to the near infrared range: 2,4,5,7-Tetranitrofluorene (TNF) as a unique electron acceptor

Fourteen dyes based on 2,4,5,7-tetranitrofluorene (TNF) as the electron acceptor have been designed and prepared in a one-step synthesis. By modifying the electron donor, optical properties of the dyes could be efficiently tuned and an absorption ranging between 450 nm and 700 nm could be determined by UV–visible absorption spectroscopy. To get a deeper insight into the optical properties, solvatochromism of the fourteen dyes has also been examined. For all dyes, a positive solvatochromism was determined using different solvent polarity scales such as the Kamlet-Taft and the Catalan empirical scales. Finally, electrochemical properties were also examined, and a comparison of the electrochemical and optical bandgaps could be established. Theoretical calculations were also performed to characterize the different dyes.

Reappraisal of Empirical Solvent Polarity Scales for Organic Solvents

AbstractCorrelations of Reichardt'sET(30), the CatalánSdP(solvent dipolarity),SP(solvent polarizability),SA(solvent acidity),SB(solvent basicity), Kamlet‐Taftπ* (dipolarity/polarizability),α(hydrogen bond donating ability) andβ(hydrogen bond accepting ability) polarity parameters with the molar concentration of 161 pure organic solvents are presented. Mostly, linear relationships of the polarity parameter as a function of molar concentration are obtained as long as each individual solvent class is considered separately. A physically different interpretation of theET(30), Kamlet‐Taftπ* andαas well as CatalánSAandSBparameters has been proposed. Furthermore, the Hildebrand solubility parameter in combination with the diffraction index is used for the correlation analysis with the above‐mentioned solvent parameters. It can be concluded that empirical polarity parameters derived from solvatochromic UV/Vis measurements are inherently a function of the molecular structure of the probe.

Synthesis, optical and electrochemical properties of a series of push-pull dyes based on the 2-(3-cyano-4,5,5-trimethylfuran-2(5H)-ylidene)malononitrile (TCF) acceptor

A series of chromophores was designed and synthesized using 2-(3-cyano-4,5,5-trimethylfuran-2 (5H) -ylidene) malononitrile (TCF) as the electron acceptor and differing from each other by the use of thirteen different electron donors. The different dyes were characterized for their optical and electrochemical properties and theoretical calculations were also carried out to support the experimental results. By changing the electron donor in the thirteen dyes, chromophores absorbing between 430 nm and 700 nm could be synthesized. Solvatochromism of the different dyes was analyzed in 23 solvents of different polarity and a positive solvatochromism was determined for all chromophores using the semi-empirical solvent polarity scales based on the Kamlet-Taft parameters (π *) or the Catalan parameters (SdP and SPP).

Synthesis of novel viscosity sensitive pyrrolo-quinaldine based styryl dyes: Photophysical properties, electrochemical and DFT study

We have synthesized two novel styryl dyes namely (E)-2-(2-(9-butyl-9H-carbazol-3-yl)vinyl)-3,3,8-trimethyl-3H-pyrrolo[3,2-h]quinoline (PQC) and (E)-10-butyl-3-(2-(3,3,8-trimethyl-3H-pyrrolo[3,2-h]quinolin-2-yl)vinyl)-10H-phenothiazine (PQPT). These dyes were characterized by FT-IR, HR-MS, 1H and 13C NMR spectroscopy techniques. Both dyes displayed absorption wavelength within the range of 399−427 nm. Ranging from non-polar solvents towards polar solvents, these dyes exhibited emission wavelength and Stokes shift from 487−605 nm and 85−180 nm respectively. The photophysical study of these dyes in seven solvents suggested that these dyes show positive emission solvatochromism which was investigated from Reichardt's ET (30) plot, Lippert-Mattaga graph and MacRae solvent polarity scale plots. In addition, these dyes show evidence of intramolecular charge transfer properties which were explained with the assist of Wellers, Rettig plots and ground-excited states dipole moment difference. The electrochemical properties of these dyes were investigated with the help of cyclic voltammetry and differential pulse voltammetry. Viscosity sensitivity studies were also performed on the synthesised dyes in the methanol and polyethylene glycol 400 system with varying viscosity of the solvent system. The thermal properties of these dyes were investigated using TGA and DSC analysis, which shows that dyes were thermally stable up to 200 °C. The theoretical photophysical properties of these dye molecules was explored by density functional theory (DFT) along with the time dependent density functional theory (TD-DFT).

Characterization of short-range molecular interaction by empirical solvent polarity scale to analyze the Kerr effect of nematic liquid crystals in the isotropic phase

It is well known that a relatively large Kerr effect in the isotropic phase of nematic liquid crystals (NLCs) is related to the existence of short-range ordering (SRO). Thus, the conversion of the long-range ordering (LRO) behavior in the nematic phase to the SRO in the isotropic phase of NLCs can characterize the nonlinear electro-optic Kerr effect. To show conversion from LRO to SRO, we employ an empirical solvent polarity scale (ETN). Interestingly, ETN originates from the solvatochromic polarity (SP) parameters, which demonstrates the quantitative value for describing the molecular interaction in each temperature point, even in the isotropic phase of NLCs. Our results show that the higher ETN value leads to a larger Kerr constant (B) owing to the larger short-range molecular interaction between rigid rod-like NLCs. To demonstrate a linear relationship of the B value with the ETN and SP parameters, a new correlation is introduced for the first time. Our investigations and newly introduced parameters strongly indicate that short-range molecular interactions still exist in the isotropic phase of NLCs, even when the macroscopically observable LRO behaviors disappear.