Light, Metal, and CO Photorelease

Carbon monoxide (CO) is an endogenous signaling molecule with promising therapeutic potential, stimulating the development of carbon monoxide-releasing molecules (CORMs). When activated by light, photoCORMs enable controlled CO delivery with temporal and spatial regulation. This lecture explores how metal centers, ligand architecture, and electronic structure govern CO photorelease from transition-metal carbonyl complexes, focusing on Mn(I) and Re(I) tricarbonyl compounds. Experimental studies combining spectroscopy, mass spectrometry, crystallography, and photochemical assays reveal the formation of biscarbonyl intermediates and structural rearrangements following CO dissociation. In Mn(I) complexes, CO release may promote coordination of previously uncoordinated donor atoms, significantly influencing the photochemical pathway. DFT and TD-DFT calculations provide molecular-level insights into excited-state structures, dissociative pathways, spin–orbit coupling, and intersystem crossing. Understanding these processes enables the rational tuning of the wavelength, efficiency, rate, and extent of CO release, contributing to the development of next-generation photoCORMs for controlled CO delivery and potential biomedical applications.