Visible light-induced CO-release from manganese carbonyl complexes based on Schiff base ligand

Three manganese carbonyl complexes [Mn(CO)(3)(py(CH=N)ph - X)Br], where X=Cl (1), Br (2), I (3), containing Schiff base ligands were synthesized by a one-step method using manganese pentacarbonyl bromide, 2-pyridine formaldehyde, and halogenated aniline. They were characterized by NMR, X-ray single crystal diffraction, IR spectrum, UV-Vis spectrum, and fluorescence spectrum. These complexes were stable under non-illumination, but they could decompose to release CO under visible light (LED blue, green, and red light), which can be used as photo-induced carbon monoxide release molecules (photoCORMs). The CO release rate could be conveniently controlled by selecting different lights. It has been shown that blue light was the most effective light source to promote the decomposition of these complexes to release CO. The differences in the electronic effects of the halogenated ligands in these complexes also contribute to the differences in their reaction rates. In addition, the kinetic analysis of CO release shows that the process conforms to the first-order kinetic model. The carbon monoxide release of complex 3 was also studied by standard myoglobin assay, showing that deoxymyoglobin was able to capture the released CO. Although the cytotoxicity of these complexes itself reached the micromolar level, the cell compatibility under light was significantly improved, rising to nearly 100 micromolar levels. These complexes had fluorescent properties, emitting a certain intensity of fluorescence in a range of 500-700 nm at the excitation wavelength of 450 nm, which can be used as fluorescent markers to monitor the distribution of release agents and CO release in cells or organisms.