Photosensitized singlet oxygen and oxygen complexes in the occurrence and change of spatially inhomogeneous luminescence in solutions of anthraquinone

Abstract

The purpose of the present work is an analysis of the processes leading to inhomogeneous in space and time luminescence (the so-called luminescent spatial and temporal structures), which is observed in the visible region (l_max= 490 нм) with ultraviolet (UV) radiation of anthraquinone in oxygenated solutions and polymer matrices. Experimentally recorded luminescence is attributed to the photoproduct: ketil radical of anthraquinone, the concentration of which in the course of photochemical reactions initiated by UV radiation periodically increases and decreases in different and isolated points of the reaction space. In the paper the importance of the quenching reaction of triplet states of anthraquinone molecules with oxygen О₂(³Σ^-_g ) was justified, the possibility of generating of singlet oxygen O₂(¹Δ_g) at large distances from the reaction center due to the transfer of vibronic excitation to the solvent molecule was discussed and the significant role of sensitized singlet oxygen in the redistribution of concentrations of reagents and photoproducts was emphasized. A model was proposed for the emergence and development of the spatially inhomogeneous luminescence of anthraquinone solutions, including photosensitized formation of singlet oxygen and diffusion of the oxygen complexes with solvent molecules. The main advantage of the proposed model, which takes into account the occurrence and presence of singlet O₂(¹Δ_g)  oxygen, is in the opportunity not only to explain the experimentally observed effects of the emergence and development of spatial-temporal structures, but also to predict the conditions of change, the nature of the behavior of the initial stage of their development and the final result. The discussed in the work dependence of the phenomenon on the concentration of dissolved oxygen can be used in sensory applications.