Hemin‐Derived Porphyrins as Heterogeneous Photosensitizers: Role of the Free‐Base and Metal Centers in Singlet Oxygen Generation

The generation of singlet oxygen ( 1 O 2 ) through photosensitization is an attractive strategy for sustainable oxidation processes. In this work, a series of hemin‐derived porphyrins, including the metal‐free ligand and Zn(II), Cu(II), and Co(II) complexes, were supported onto Colour Catcher material by immersion in a basic porphyrin solution. The heterogeneous photosensitizers were obtained by ionic anchoring, whose efficiency increased with immersion time. Among the species investigated, hemin exhibited the fastest adsorption kinetics and the highest loading, whereas the metal‐free ligand showed the lowest uptake. All materials were characterized by scanning electron microscopy/energy‐dispersive X‐ray spectroscopy, inductively coupled plasma optical emission spectroscopy, and UV–visible spectroscopy and the photocatalytic performance was investigated in the oxidation of 1,5‐dihydroxynaphthalene (1,5‐DHN) as a model probe for 1 O 2 generation. Initial reaction kinetics were determined, highlighting significant differences in activity depending on the metal center with the heterogenized metal‐free porphyrin exhibiting the best performance. The reaction medium was found to play a crucial role. In aqueous mixtures, the reaction started relatively faster due to a rapid 1 O 2 production, though being progressively inhibited with irradiation time. Differently, in acetonitrile, a higher 1,5‐DHN conversion degree was achieved although with slower initial rates. Preliminary tests on the oxidation of differently substituted benzaldehyde to benzoic acid confirmed the effective formation of 1 O 2 .