Carbonyl Amine/Schiff Base Ligands in Manganese Complexes: Theoretical Study on the Mechanism, Capability of NO Release

A compound having the capability of releasing NO upon exposure to visible or near-infrared (vis or NIR) light could be a potential candidate for photodynamic therapy (PDT), which is significant for humans. Here, we investigated a series of Mn(II) complexes (a–d) based on density functional theory (DFT) to illuminate the mechanism of their behavior of releasing NO. Their structural, spectroscopic, and photodissociable properties were calculated by quantum theoretical methods to give a detailed and warranted explanation of the performance of releasing NO. The results indicate that, for a–d, releasing NO was attributed to the electron transfer from dyz/dxz(Mn) orbitals to π*(NO) orbitals at the second excited triplet state (T2). Importantly, we confirmed the finding in the experiment that d could release NO upon exposure to the NIR region and, thus, may be a best candidate for PDT in a–d. Therefore, to take d for example, the analyses of the potential energy curves (PECs) of difference states and electron de...