Visible-light photoredox catalysis of polydopamine with triethanolamine in water.

Polydopamine (PDA), a synthetic melanin, has recently emerged as a photoreactive material, contrasting with its conventional role in photoprotection. In particular, its photochemical reactivity under visible light offers a new perspective on the role of melanin and opens up potential applications in biomedical engineering and energy conversion. However, the mechanism of the visible light-induced reactions is still not well understood, necessitating further systematic investigation. To address this challenge, we carefully investigated its photoredox catalysis under visible-light irradiation, focusing on electron transfer processes in the presence of triethanolamine as an electron donor. We explored various aspects, including its size-dependent reactivity, electrochemical and photophysical properties, and the characterization of generated radical species. Furthermore, we sought to optimize photoinitiated polymerization under various reaction conditions, such as different concentrations, monomers, and atmospheres. The use of water as a solvent is generally considered safe and poses minimal risk to human health and safety compared to many organic solvents. These results are crucial for advancing the understanding of melanin's photoredox catalytic mechanism and for developing innovative biocompatible photoreactive materials.