Novel Arenimidazolyl Porphyrins for Use in the Photocatalytic Oxidation of Organic Substrates

The ability of porphyrins and their derivatives to generate reactive oxygen species (ROS) upon irradiation allows these compounds to serve as mild and highly selective agents for various photooxidation reactions. The wide range of possible modifications at the periphery of the heterocycle, as well as variation of the coordinated metal cation, enables precise tuning of the photophysical properties of the macroheterocycles and increases the rate of singlet oxygen generation under light exposure.

In this research, we present a novel synthetic route to β-arenimidazolylphenyl porphyrins. A series of target compounds was synthesized and fully characterized using standard physicochemical methods. We employed a set of tetraarylporphyrins to investigate the influence of meso-substituents on the reaction pathway, solubility, and photocatalytic efficiency.

In order to evaluate the effect of the arenimidazolyl fragment on the photocatalytic activity of porphyrins, we used the oxidation of sulfides as a model reaction. Even with a very low catalyst loading (0.5 × 10⁻⁴ mol %) and under blue-light irradiation (λ = 430-505 nm, 5 W), complete substrate conversion was achieved with >99% selectivity toward the corresponding sulfoxides. We also measured the photostability of the obtained free-base porphyrins. No significant photodegradation was observed for more than five hours of irradiation, which is comparable to the performance of existing industrial photocatalysts.

The high efficiency in model photooxidation reactions, combined with excellent photostability, allows us to consider target substances as potential photocatalysts in production of medicinal substances, bearing sulfoxide functional groups.

This work was performed with financial support from the Ministry of Science and Higher Education of the Russian Federation.