Illumination of sulfonated poly(ether etherketone), SPEEK, and polyvinyl alcohol, PVA, in the presence of thionine (Th) results in systems exhibiting reversible redox processes. Efficient reduction of thionine takes place when SPEEK/PVA/Th films are exposed to 350 nm photons. This photoreduction process involves radicals of SPEEK (sensitizer), which lead to the formation of semithionine (thionine radical) as an intermediate, and finally leucothionine. Thionine is initially photoreduced (first 40 s – 50 s of illumination) via a zero-order rate law with a rate constant of k = 1 x 10-5 Ms-1. The reaction seems to follow dispersive kinetics after 40 s - 50 s of photolysis. Reformation of thionine is very slow and takes 30-45 days for completion, but addition of distilled water (3 ml) to illuminated films accelerates the reaction which now proceeds via first-order kinetics with k = 2.37 s-1. Unlike films, the Th photoreduction in SPEEK/PVA degassed solutions followed zero-order kinetics throughout the decay with k = 2 x 10-6 Ms-1. In the presence of air, the Th reformation follows zero-order kinetics with a rate constant much lower than that of the reduction process (k = 3.3 x 10-8 Ms-1). Th reduction and reoxidation was reversible in both SPEEK/PVA/Th films and solutions for more than 8 consecutive illumination cycles.

Light-induced reversible reactions in SPEEK/PVA films and solutions containing thionine

256th National Meeting (2018)

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