Mediating Photochemical Reaction Rates at Lewis Acidic Lanthanides by Selective Energy Loss to 4f-Electron States

Manifesting chemical differences in individual rare earth (RE) element complexes is challenging due to the similar sizes of the tripositive cations and the core-like 4f-shell. We disclose a new strategy for differentiating between similarly-sized Dy3+ and Y3+ complexes through a tailored photochemical reaction, where the f-electron states of Dy3+ act as an energy sink. Complexes RE(hfac)3(NMMO)2 RE = Dy (2-Dy), Y (2-Y), hfac– = hexafluoroacetylacetonate, NMMO = N-methyl-morpholine-N-oxide, synthesized from their hydrated precursors, showed variable rates of oxygen atom-transfer to triphenylphosphine acceptor under UV irradiation, as monitored by 1H- and 19F-NMR spectroscopies. Ultrafast transient absorption spectroscopy identified the excited state(s) responsible for the photochemical OAT reaction. Sensitization pathways leading to excited state deactivation in 2-Dy through energy transfer to the 4f-electron manifold ultimately slow the reaction at that metal cation. The measured rate differences between the open- and closed-shell Dy3+ and Y3+ complexes demonstrates that using established principles of 4f-ion sensitization may deliver new, selective modalities for differentiating the elements that do not depend on cation size.