UC Santa Barbara

Ruthenium (Ru) polypyridyl complexes have been extensively used as optical probes, photoactivated anticancer agents, and photocages for biologically active ligands. In this study, Ru²⁺ polypyridyl complexes were investigated as photoreleasing agents for the H₂S donor GYY4137. Four complexes of the general formula cis-[Ru(NN)₂(GYY4137)]⁺, where NN = 2-2'-bipyridine (bpy), 2,2'-biquinoline (biq), 4,4'-methoxy-2,2'-bipyridine (dmobpy), and 4,4'-di-tert-butyl-2,2'-bipyridine (dtbpy), were synthesized and characterized by NMR spectroscopy and X-ray crystallography. The photochemical reactivity of these complexes was investigated, revealing that ligand photodissociation occurs in a two-step reaction. For these reactions, long-lived intermediates where the bidentate ligands attain a monodentate coordination mode could be detected. Furthermore, the ancillary diimine ligands dictated the identity of the final photoproducts observed, with some compounds ejecting GYY4137 and others ejecting the diimine ligand. The measurements of the photochemical quantum yields reveal trends in these values depending on the planarity enforced by the diimine ligands on the central complex. Density functional theory (DFT) calculations were carried out to probe the influence of complex structure on the ligand ejection process. These studies provide insight into the photoreactivity of Ru²⁺ polypyridyl complexes bearing GYY4137, results that are of relevance more broadly for the use of these scaffolds to release anionic sulfur-containing ligands.