Micellar effects on dye sensitized photooxidation of phenothiazine

Abstract

Methylene blue sensitized photooxidation of phenothiazine (PTH) in sodium dodecylsulphate, cetyl trimethylammonium bromide and brij-35 in methanol-water, ethanol-water and acetonitrile-water gives phenothiazine-3-one (PTN) and phenothiazine sulphoxide as the products at low conversion. A small shift in the λmax indicates the formation of an additional product, which is destroyed during the separation. An inverse relationship between log Φ (Φ= quantum yield of PTN formation) and 1/Є₀ (Є₀ = dielectric constant of the medium) supports the participation of singlet oxygen (¹O₂) at low [PTH]. A mechanism consistent with the results showing the participation of ¹O₂ at low [PTH] and electron transfer-exciplex formation at high [PTH] is postulated. The formation of phenothiazine sulphoxide has been suggested to be through the phenothiazinyl radical.