This article investigates the methylene blue (MB) dye reduction on a specially designed optical bench under the radiation of 656 nm through the oxidation of p-phenylenediamine (PPDA), an extreme sensitizer in a methanolic solvent. The oxidation of PPDA leads to the formation of polyaniline, a conductive polymer that is widely used in dye-sensitized applications and environmental remediation. Photoredox reaction studied on several acidic pH using acetate buffer and parameters (i) acidity (H_o) at the fixed concentration of dye (ii) various concentrations of PPDA, and (iii) temperature. The quantum yield was found to be a function of PPDA concentration, acidity, and temperature. It was concluded that a triplet transition state is involved in leuco dye formation and photo-oxidation of aromatic amine. It was also found that two equilibria were established between H⁺, dye, and PPDA (MB⁺. PPDA) and one form of triplet state of methylene blue with reductant PPDA. It was suggested that PPDA absorbed a photon of light and released 2 protons, which were abstracted by MB_T, resulting in the bleaching of dye or leuco dye formation.

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