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.