ÉTUDE EN SPECTROSCOPIE PAR ÉCLAIR DES COLORANTS THIAZINIQUES EN SOLUTION AQUEUSE

Abstract

Abstract— p K values of ionisation equilibrium of thiazines dyes in their triplet state have been measured in aqueous solutions by spectroscopy. The triplet‐triplet absorption bands, in the red part of the spectrum, are given for thionine, azurs and methylene blue. It is shown that, in the pH range 4–9, the equilibria investigated correspond to a second protonation of thiazines dyes that occurs in the triplet state: 3 TH + + H + → 3 TH 2 2+ designating by 3 TH + the thiazine cation similar to the species stable in neutral aqueous solutions.