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Cyclic voltammetric investigations have been performed on the clean glassy carbon electrode (GCE) at (25 ± 0.1) °C on five progressively alkylated thiazine dyes, namely, thionine (Th), methyl thionine (Azure C), dimethyl thionine (Azure A), trimethyl thionine (Azure B), and tetramethyl thionine (methylene blue) in water, water−ethanol, and water−Triton X-100 media. Diffusion coefficient values of the dyes, measured from the electrochemical data in different media, are clearly influenced by the effect of progressive alkylation to the thionine moiety along with the solvent property. In aqueous media the values of diffusion coefficient fall in the range of (2.66·106 to 5.70·106) cm2·s−1, whereas in presence of ethanol and Triton X-100 the rather lower ranges of (1.16·106 to 3.70·106) cm2·s−1 and (0.76·106 to 1.80·106) cm2·s−1 are observed, respectively. At higher pH’s the voltammograms display cathodic and anodic post/prepeaks which are the characteristics of the strong adsorption of reactants and/or product...