Thiosemicarbazone‐Based Ni(II) Complexes as Photocatalysts for LED‐Driven Free Radical Polymerization

Currently, 3 d metal complexes have attracted considerable attention as photocatalysts in photopolymerization reactions, representing a viable alternative to noble metals. In this work, two Ni(II) thiosemicarbazone (TSC) complexes bearing different substituents, methyl and phenyl, [Ni(N,N,S‐TSC) (4‐NH 2 Py)] (Ni‐TSC Me and Ni‐TSC Ph ), were synthesized via the reaction of [NiCl 2 (PPh 3 ) 2 ] with the corresponding TSC ligand, followed by coordination of 4‐aminopyridine (4‐NH 2 Py). The resulting complexes were fully characterized by FTIR, UV–Vis, NMR, elemental analysis, and ESI mass spectrometry. Their performance as photocatalysts was investigated in photoinitiating systems containing diphenyliodonium hexafluorophosphate (Iod) and ethyl 4‐(dimethylamino)benzoate (EDB) amine for the free radical photopolymerization of trimethylolpropane ethoxylate triacrylate (TMPETA). The absorption, fluorescence, and electrochemical properties were evaluated to provide deeper insight into their photocatalytic activity, reactivity, and the proposed reaction mechanism. Both complexes exhibited enhanced performance under UV irradiation, while Ni‐TSC Me maintained remarkable photocatalytic activity under both UV and violet light. Furthermore, the interaction between the Ni(II) complexes and the additives was investigated through photolysis experiments under UV light and free energy change calculations, which served as key parameters in proposing a reaction mechanism.