Peculiarities of solvatochromism of 4-[[(2,4-dinitrophenyl)methylene]imino-2,6-diphenyl]phenol and Reichardt’s dye. DFT calculations

Abstract

One of the current directions of development of modern physical chemistry is the working out of sensor devices and molecular probes for the study of various properties of solutions, colloidal systems and biological objects. The latter include solvatochromic dyes, which, thanks to Reichardt's classic works, have found wide application for quantitative assessment of the solvating ability of individual and, to a lesser extent, mixed solvents of various nature. The different behavior of Reichardt and 4-[[(2,4-dinitrophenyl)methylene]imino-2,6-diphenyl]phenol dyes in pure water and mixed water-organic solvents, when their composition is changed, indicates that their electronic structure undergoes a fundamental change during the transition from the ground state to the first excited state. The aim of the work was to study and compare the HOMO and LUMO structure of the standard Reichardt betaine dye and the 4-[[(2,4-dinitrophenyl)methylene]imino-2,6-diphenyl]phenol dye using the stationary and time-dependent density functional theory (DFT). It is proved that the 4-[[(2,4-dinitrophenyl)methylene]imino-2,6-diphenyl]phenol dye has two active exchangeable solvation centers and therefore has an excellent solvation mechanism, at least in aqueous solution, compared to Reichardt dye, which should appear upon its solvation also in mixed water-organic solvents with a high water content in them.