Iron(II)–Schiff Base Complexes as Photocatalysts for Controlled Radical Photopolymerization under Light Emitting Diode Irradiation

Abstract

Photocatalysts, particularly metal‐based complexes, have gained significant attention in photoredox catalysis, enabling controlled radical photopolymerization (CRP2) under mild irradiation conditions, such as sunlight or LED bulbs. Herein, three Fe(II) complexes— Fe II Salen , Fe II Saloex , and Fe II Salophen —bearing nonsymmetrical Schiff base ligands are synthesized and designed for potential application in CRP2. The complexes were characterized using fourier transform infrared spectroscopy (FTIR), UV‐Vis, and fluorescence spectroscopy; matrix‐assisted laser desortion ionization time‐of‐flight (MALDI‐TOF) mass spectrometry; and elemental analysis. Additionally, density functional theory and time‐dependent density functional theory calculations are conducted to extract key structural, electronic, and excited‐state properties. The catalytic performance of these Fe(II) complexes in the CRP2 of methyl acrylate (MA) is evaluated under different conditions, using ethyl α ‐bromophenylacetate as the initiator and triethylamine as the electron donor. The photopolymerizations proceed efficiently, yielding polymers with controlled molecular weights and narrow molecular weight distributions. Among the tested photocatalysts, Fe II Saloex exhibits the best performance, achieving high conversion and low polydispersity under LED irradiation. Furthermore, a mechanism is proposed based on spectroscopic analyses and literature data.