Understanding Solvation: Comparison of Reichardt’s Solvatochromic Probe and Related Molecular “Core” Structures

Abstract

The compound 2,6-diphenyl-4-(2,4,6-triphenylpyridinium-1-yl)phenolate, p-RB, shows distinct colors in different solvents (solvatochromism). The compound 4-(pyridinium-1-yl)phenolate, p-CB, represents the part of p-RB which is responsible for this phenomenon. We compared the solvatochromism of both compounds and also the structurally related 2-(pyridinium-1-yl)phenolate, o-CB, and (2,4-dimethyl-6-(2,4,6-triphenyl-N-pyridinium-1-yl)phenolate, o-RB. In pure solvents, plots of the empirical solvent polarity parameter [E T (probe), kcal/mol] of the different probes correlate linearly with slopes close to unity. That is, these probes are similarly sensitive to specific and nonspecific interactions with the solvents. The solvatochromism of p-CB and o-CB was studied, for the first time, in binary mixtures of water with dimethyl sulfoxide (DMSO) and 1-propanol (1-PrOH). The dependence of E T (probe) on mixture composition was nonideal due to preferential solvation of the probe by one component of the binary solvent mixture. We treated our solvatochromic data using a solvent-exchange model that considers formation of the complex solvents [HOH•••OS(CH 3 ) 2 ] and [HOH•••O(H)-C 3 H 7 ]. The model applies satisfactorily to our data and shows the importance to solvation of hydrogen-bonding and hydrophobic interactions. The preferential solvation of (more hydrophobic) p-RB is more pronounced than that of p-CB or o-CB. The solvent complex [OH 2 •••O(H)-C 3 H 7 ] is more efficient than [OH 2 ••• OS(CH 3 ) 2 ] because of more possibilities of hydrogen bonding.

Poly(vinyl pyridine) and Its Quaternized Derivatives: Understanding Their Solvation and Solid State Properties

“…Studying these interactions experimentally has various limitations, many of which can be overcome using suitable probe molecules, which are sensitive to minute changes in their solvation microenvironment (cybotactic region) [ 63 , 64 , 65 , 66 , 67 ]. Herein, we employ the intensely sensitive solvatochromic betaine of Reichardt [ 68 ] in order to unravel the role of hydrogen bonding in solutions of PVP and PVPQ in binary solvent mixtures consisting of H 2 O and DMSO. Two main criteria of choice of these two solvents were considered; firstly, the solubility of the polymers and secondly, the involvement of protic and non-protic solvents in the investigated mixtures.…”

“…As Reichardt’s betaine can act as an indicator of solvent polarity in DMSO/H 2 O mixtures (the preferential solvation of Reichardt’s betaine in DMSO/H 2 O mixtures has been examined thoroughly in the past [ 68 ]) alterations of the solvation effect in solutions of any of the polymers PVP or PVPQ in DMSO/H 2 O mixtures are expected to be detectable through the solvatochromism of Reichardt’s betaine.…”

Micro- vs Macrosolvation in Reichardt’s Dyes

“…Understanding solvent interactions of Reichardt’s dyes has been subject to multiple experimental ,− and theoretical investigations. − Hydrogen bonding and specific interactions were recognized as the main cause for deviations in the empirical correlations between solvent shifts and macroscopic properties . For example, 1b fails to show a linear correlation between the transition energy and E T N in the full range of solvents but shows good correlations in the subsets of polar and apolar solvents .…”

Designing Safer Solvents to Replace Methylene Chloride for Liquid Chromatography Applications Using Thin-Layer Chromatography as a Screening Tool

“…The Kamlet-Taft parameters, Hansen solubility parameters (HSP), and the Schneider solubility triangle are three such systems that have been used to evaluate the solubility of organic molecules such as APIs [10][11][12]. The Kamlet-Taft parameters utilize Solvatochromic data based on Solvatochromism, a phenomenon where specific compounds (probes) adsorb different wavelengths of light and thus show different colors [13]. In the case of solubility, the color of the probe changes based on the solvent in which it resides, providing information about the solvation ability of the solvent [13,14].…”

“…The Kamlet-Taft parameters utilize Solvatochromic data based on Solvatochromism, a phenomenon where specific compounds (probes) adsorb different wavelengths of light and thus show different colors [13]. In the case of solubility, the color of the probe changes based on the solvent in which it resides, providing information about the solvation ability of the solvent [13,14]. The Kamlet-Taft system contains the parameters α (hydrogen bonding donating ability), β (hydrogen bonding accepting ability), and π * (polarizability), which are used in combination to predict solubility results [7].…”