Alternative procedures for the green synthesis of 3,7-bis(n,n-(2hydroxyethyl)amino)phenothiazinium dye

Two experimental procedures implying mechanochemical and ultrasounds assisted protocols were assessed as alternatives to the classical synthesis of the title MB analogue, based on the substitution of the phenothiazinium tetraiodide with diethanolamine nucleophile. These greener alternatives required a much shorter reaction time and consequently less energy consumption. The sonochemical procedure gave a crystalline reaction product demanding a facile purification. UV-vis spectroscopic analysis emphasized the optical properties of the 3,7bis(N,N-(2-hydroxyethyl)amino)phenothiazinium dye characterized by an intense absorption maxima situated at 663 nm and weak fluorescence emission in aqueous solution (quatum yield 0.7% relative to methylene blue standard) with the emission maxima situated at 685 nm (Stokes shift 484 cm(-1)). The solid state structure of the dye was determined by X-ray diffraction.