Assessment of the composition of aqueous-organic mixtures by solvatochromism of 4-[(octylylpyridinium)ethenyl]phenolate dyes

Abstract

This work deals with the investigation of assesment of the composition of aqueous dimethylformamide mixtures based on solvatochromic shift of some 4-hydroxystyryl dyes. The purity of the studied dyes was tested. Spectrophotometrical, protolytycal and solvatochromic properties of the ОР4-MS and OP4-DMS dyes were investigated. The transformation from the protonated to merocyanine form is accompanied by bathochromic shift. Absorption maxima of the cationic and merocyanine forms in aqueous solutions and acidity constants (pKa) of the investigated dyes have been determined by specrophotometric method. Ratiometric functions were investigated for the selection of the best quantitative parameter that binds the composition of the mixtures (water content) with solvatochromic shifts of the dyes. Correlation coefficients (R2) are greater than 0.99. It is noted that the color of merocyanine forms of dyes depends on the composition of water-organic solutions ranging from pink to blue in the transition from water to a pure solvent, which allows to set the composition of the mixtures. The possibilities of determining the composition of mixed solutions using colorimetric scales and by processing spectrophotometric data are discussed.