Proton transfer in organic dyes: study and application

Abstract

The process of proton transfer between the dye and the solvate shell forms an equilibrium distribution of different charge species. In addition to the acidity of the solution (pH), this equilibrium is influenced by temperature and the presence of inorganic ions. Equilibrium shift can be quantified due to the difference in the spectral characteristics of ionic forms.
Photoexcitation of the dye can shift the equilibrium to the acidic or basic region, and the substance acquires the properties of a photoacid or photobase. The fluorescence signal of the molecules contains additional information about the relationship between the rates of fluorescence and equilibrium in the excited state. Establishing a relationship between the spectral characteristics of a dye and the dynamics of its intra- and intermolecular relaxations is both a complex and promising task for the development of sensor applications.
The talk considers in detail fluorescein (including fluorescein isothiocyanate), which is subject to three-step dissociation in a wide pH range. Using a set of computational (Van't-Hoff formalism, Forster cycle, kinetic approach) and experimental (steady-state and time-resolved) methods, the fluorescence characteristics of all ionic forms (dianion, monoanion, neutral quinoid, and cation) were determined for the first time. Correlations between the fluorescent ratiometric signal of fluorescein and the concentration of phosphate ions and solution temperature were revealed. These relations in the physiological pH range can be required for non-contact probing in biomedical application.

The work was supported by the Russian Science Foundation, project 22-22-00724

Speaker

Evgenia Slyusareva
Siberian Federal Universuty
Russia

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