Singlet oxygen generation in hybrid porphyrin/DOPA-melanin coatings

Melanin-like coatings derived from the spontaneous oxidation of catecholamines represent an attractive and versatile platform for surface functionalization strategies. However, the intrinsic broadband absorption of melanin-like polymers and their scavenging behavior toward reactive oxygen species often limit their use in applications requiring efficient photochemical outputs. Herein, we report a practical strategy for obtaining a photodynamically active hybrid coating through the self-polymerization of L-DOPA in aqueous solution on an ordinary glass substrate, in the presence of the cationic 5,10,15,20-tetrakis(4-N-methylpyridyl)porphyrin, H2T4, acting as a photosensitizer. The resulting hybrid H2T4/L-DOPA melanin-like film, spontaneously formed on the glass surface, generated singlet oxygen in organic media, such as deuterated methanol, whereas no singlet oxygen was observed in aqueous media, such as deuterated water. This constraint was overcome through a post-functionalization step that increased the porphyrin loading and enabled the singlet oxygen generation in deuterated water. Overall, this two-step functionalization strategy provides a straightforward approach to obtaining melanin-like coatings that produce singlet oxygen in aqueous environments, thereby supporting the development of light-activated antibacterial surfaces.