Determination of a Solvent Hydrogen-Bond Acidity Scale by Means of the Solvatochromism of Pyridinium-N-phenolate Betaine Dye 30 and PCM-TD-DFT Calculations

Abstract

Empirical parameters of solvents describing their hydrogen-bond (HB) acidity (e.g., the Kamlet-Taft α parameter) are often difficult to determine for new solvents because they are not directly related to a single definition process. Here, we propose a simple method based on one probe, the betaine dye 30, and one reference process, the solvatochromism of this dye, measured by its first electronic transition energy, ET(30). These ET(30) values are calculated within the time-dependent density functional theory framework, using a polarizable continuum solvent model (PCM). The part of ET(30) values that is not included in the PCM calculation is taken as the HB component of the measured ET(30) values, allowing us to deduce a solvent HB acidity parameter α1. The validity of this simple model is assessed by good linear correlations between α1 and a variety of solute properties mainly depending on the solvent's HB acidity. The quality of fit observed with α1 is at least comparable with that obtained by previous solvent HB acidity scales. The simplicity of our method is illustrated by the determination of α1 and of its companion, the electrostatic solvent parameter ES, for some new green solvents derived from glycerol.

Solvatochromic behavior of dyes with dimethylamino electron-donor and nitro electron-acceptor groups in their molecular structure

“…Table shows the calculated E T values in kcal mol −1 for the dyes in the gas phase and in seven different solvents. Although PCM calculations do not provide good results for solvents with medium to high polarity and TD‐DFT calculations tend to overestimate the internal charge‐transfer transition‐energy of solvatochromic dyes, the results are good. The data show a reversal in the solvatochromism for all dyes, as shown in Fig.…”

On‐chip electromembrane extraction of acidic drugs

“…To our knowledge, only one single paper is available in the literature describing on-chip EME of acidic drugs [20], where simultaneous extraction of acidic and basic drugs was proposed, achieving the best extraction efficiency with 1-octanol as SLM for the acidic analytes. 1-Octanol is optimal in terms of hydrogen bonding acidity (␣), hydrogen bonding basicity (␤), and dipolarity-polarizability ( * ) [21]. However, due to slight water solubility (1.2 g/L) it may not be stable under flow conditions and, in our experience, its use as organic solvent in microfluidic chip devices should be, therefore, avoided.…”

Exploring the Solvatochromism of Betaine 30 with Ab Initio Tools: From Accurate Gas‐Phase Calculations to Implicit and Explicit Solvation Models

“…Eventually,t hough we treat this point in the following, we note that the gas-phase vertical transition energies determined with CC2, that is, 1.127 eV,c orresponds to an R T (30) value of 26.0 kcal mol À1 that is in reasonable agreement with the most recent extrapolationf rom experimentald ata (30.1 kcal mol À1 ). [23] The CAM-B3LYP value is significantly too large, and this overestimation is indeed common for TD-DFT applications devotedt osimilardyes. [84,85]…”

“…According to Renge [20] and Matyushov et al [21] a significantly increases (+ 880 [20] or + 412 a.u. [21] )w hen going from the GS to the ES, whereas Catalµna nd co-workers [27] suggested an egligible change in a upon excitation.L ikewise, in the absence of directm easurements, the position of the gasphase absorption maximum can be predicted by using extrapolationso ft he condensed-phase measurements only.S uch extrapolations are sensitive to the applied approach and ap anel of values were reported in the literature: l = 709, [20] 951, [23] 1043, [24] 1053, [25] 1059 [26] and 1083 nm. [27] Of courset he presentw ork is not the first theoretical contribution dedicated to B30 as the experimental measurements inspired several modelling studies and we survey thesep revious investigations here.…”

“…Cerón-Carrasco et al calculated the excitation energies of B30 in 31 non-hydrogen-bond-donating and 55 hydrogen-bonddonating solvents, in aj oint theoretical-experimental effort aiming to determine the electrostatic and hydrogen-bond acidity contributions to E T (30). [23] To this end, they selected the CAM-B3LYP/6-31 ++G(d,p) methoda nd two versions of the PCM solvent model.L aurence et al applied as imilar protocol for estimating electrostatic empirical parameters for about 300 solvents. [48] In ac ombination of experimental measurements and theoretical calculations, Kharlanov and Rettig [15] and Catalµne tal.…”