title: Phototransformation of anthraquinone-2-sulphonate in aqueous solution.
abstract: Anthraquinone-2-sulphonate (AQ2S) is a triplet sensitiser that has recently been used to model the photoreactivity of chromophoric dissolved organic matter (CDOM). We show that the photolysis quantum yield of AQ2S under UVA irradiation varies from (3.4 ± 0.2) × 10(-3) at μM AQ2S levels to (1.8 ± 0.1) × 10(-2) at 3 mM AQ2S (μ±σ). This trend is consistent with a combination of direct phototransformation and transformation sensitised by a photogenerated reactive species. In both cases a transient water adduct of AQ2S would be involved. Depending on the initial quinone concentration, the adduct could undergo transformation, give back ground-state AQ2S or react with it. The prevalence of the latter process at high AQ2S concentration would account for the increased values of the photolysis quantum yield. When using AQ2S as a triplet sensitiser, one should not exceed an initial concentration of 0.1 mM. Under the latter conditions the sensitised process is negligible compared to the direct photolysis, providing a simpler system to be studied, and the photolysis quantum yield is independent of the initial AQ2S concentration. This paper also shows, by adoption of density functional theory calculations, that the triplet state of AQ2S has most of the spin density localised on C[double bond, length as m-dash]O, analogous to other photoactive quinones, which accounts for the oxidising character of the triplet state that tends to be reduced to a semiquinone radical.
authors: Dipartimento di Chimica, Università degli Studi di Torino, Via Giuria 5, 10125 Torino, Italy.
authors: Andrea
authors: A
authors: Bedini
authors: Elisa
authors: E
authors: De Laurentiis
authors: Babita
authors: B
authors: Sur
authors: Valter
authors: V
authors: Maurino
authors: Claudio
authors: C
authors: Minero
authors: Marcello
authors: M
authors: Brigante
authors: Gilles
authors: G
authors: Mailhot
authors: Davide
authors: D
authors: Vione