Photophysical Properties of a Mn(I) Tricarbonyl PhotoCORM With 8-Aminoquinoline Ligand: Insights From Theory.

The photophysical properties of a recently synthesized photoCORM, the Mn(I) tricarbonyl complex fac-[MnBr(CO)3(AQ)] (AQ = 8-aminoquinoline), with promising cytotoxic activity against triple-negative breast cancer, have been investigated by means of density functional theory (DFT) and time-dependent DFT calculations. Simulations in various solvents (water, DMSO, THF) confirmed the Mn-CO bonds follow a Dewar-Chatt-Duncanson model, only slightly modulated by solvent polarity. The optimized computational method accurately reproduced the UV-vis spectrum, identifying the lowest energy excitations as metal-to-ligand charge-transfer (MLCT) states with minor ligand-to-ligand charge-transfer (LLCT) contributions, whose extent depends on solvent polarity. Exploration of the triplet excited-state manifold revealed several low-lying metal-centered (3MC) states accessible from the initial singlet. High spin-orbit coupling and rapid intersystem crossing rates indicate that CO photorelease occurs through efficient population of these dissociative 3MC states, especially in polar media. These findings provide mechanistic insight into the photoactivation pathway of Mn(I)-based photoCORMs and establish a robust computational framework for designing efficient CO-releasing therapeutic agents.