Multielectrochromic properties of methylene blue and phenosafranine dyes incorporated into Nafion^® film

Abstract

The electrochemical and spectroelectrochemical properties of phenosafranine (a phenazine dye) (PS⁺) and methylene blue (a phenothiazine dye) (MB⁺) immobilized into Nafion^® (Nf) film were studied in 0.5 M H₂SO₄. The PS⁺ dye was readily incorporated into Nf film containing MB⁺ or vice versa, presumably by electrostatic interaction with the free sulfonate (---SO₃^-) groups and hydrophobic interaction with the fluorocarbon moieties of the Nf film. The interaction of these dyes with the hydrophobic fluorocarbon moieties could be understood from their observed higher concentration than the available sulfonate groups in the Nf film and also from their stable redox behavior. On the other hand, thionine (TH⁺), another member of the phenothiazine family, was partially leached from the Nf film when the incorporation of PS⁺ was followed because of its weak interaction with the hydrophobic fluorocarbon moieties of the Nf film. The PS incorporated Nf film containing MB⁺ (Nf/PS⁺/MB⁺) showed two well-separated reversible redox waves at 0.22 and -0.05 V (SCE) due to the redox process of MB⁺ and PS⁺, respectively. The amount of dye molecules in the Nf film could be varied by changing the concentration of dye molecules in the immersion solution. The Nf/PS⁺/MB⁺ film showed highly stable reversible color changes upon repeated cycles of applied potentials when compared to the Nf film with incorporated TH⁺ and PS⁺ dyes (Nf/TH⁺/PS⁺). The changes in the absorbance of Nf/PS⁺/MB⁺ film were accompanied with visible reversible changes of film color, ranging from blue-red at 0.7 V to red at 0.0 V and colorless at -0.5 V(SCE) due to the reversible redox process of the MB⁺ and PS⁺ dyes in the Nf film.