UV–Vis spectroscopic study of preferential solvation and intermolecular interactions in methanol/1-propanol/acetonitrile by means of solvatochromic probes

• Four solvatochromic probes were modeled by a preferential solvation model in MeOH/1-PrOH/MeCN.
• Synergistic effects and solvent “complexes” were identified.
• Solvation “scales” for each probe in the binary and ternary mixtures were set up.
• α, β, and π* values were obtained in the ternary mixture.
• Probe/solvent/solvent interactions were characterized and rationalized.

Solvatochromic UV–Vis shifts of four indicators (4-nitroaniline, 4-nitroanisole, 4-nitrophenol and N,N-dimethyl-4-nitroaniline) have been measured at 298.15 K in the ternary mixture methanol/1-propanol/acetonitrile (MeOH/1-PrOH/MeCN) in a total of 22 mole fractions, along with 18 additional mole fractions for each of the corresponding binary mixtures, MeOH/1-PrOH, 1-PrOH/MeCN and MeOH/MeCN. These values, combined with our previous experimental results for 2,6-diphenyl-4-(2,4,6-triphenylpyridinium-1-yl)phenolate (Reichardt’s betaine dye) in the same mixtures, permitted the computation of the Kamlet–Taft solvent parameters, α, β, and π*. The rationalization of the spectroscopic behavior of each probe within each mixture’s whole mole fraction range was achieved through the use of the Bosch and Rosés preferential solvation model. The applied model allowed the identification of synergistic behaviors in MeCN/alcohol mixtures and thus to infer the existence of solvent complexes in solution.Also, the addition of small amounts of MeCN to the binary mixtures was seen to cause a significant variation in π*, whereas the addition of alcohol to MeCN mixtures always lead to a sudden change in α and β. The behavior of these parameters in the ternary mixture was shown to be mainly determined by the contributions of the underlying binary mixtures.

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