New modular manganese(I) tricarbonyl complexes as PhotoCORMs: in vitro detection of photoinduced carbon monoxide release using COP-1 as a fluorogenic switch-on probe

Five manganese(I) tricarbonyl complexes of the general formulae [Mn(bpeaNCHC6H4R)(CO)3]PF6 and [Mn(bpeaNHCH2C6H4R)(CO)3]PF6 based on the tridentate bis(pyrazolyl)ethylamine (bpea) ligand, each containing a pendant 4-substituted phenyl group with R = H, I, and CC–H, were synthesized and fully characterized, including X-ray structure analysis for three compounds. All complexes are stable in the dark in aqueous buffer for an extended period of time. However, CO-release could be triggered by illumination at 365 nm, establishing these compounds as novel photoactivatable CO-releasing molecules (PhotoCORMs). The influence of the imine vs. amine group in the ligands on the electronic structure and the photophysical behavior was investigated with the aid of DFT and TDDFT calculations. Solution IR studies on selected compounds allowed identification of intermediates resulting from the photoreaction. Finally, light-induced CO release from a model compound was demonstrated both in PBS buffer and in vitro in human umbilical vein endothelial cells (HUVECs) using COP-1 as a fluorescent switch-on probe.