Methoxy-Functionalized Coumarin-Sensitized Tris(coumarinate) Sm(III) and Dy(III) Complexes: Tunable Visible and Near-Infrared Luminescence

Abstract Achieving both high photoluminescence quantum yields(ΦLnL) and tunable visible and near-infrared (NIR) emission in organolanthanide (organo-Ln3+) luminophores remains a challenge. Herein, we report a series of ternary tris(coumarinate) Ln3+ complexes, Ln(OMe-Coum)3(2,2′-bpy) (where Ln = La (1), Sm (2), Dy (3), and Gd (4)), by utilizing 4-hydroxy-6-methoxy-3-acetylcoumarin (OMe-Coum) and 2,2′-bipyridine (2,2′-bpy) ligands. Single-crystal X-ray diffraction analysis of the Dy3+ complex reveals a solvent-free mononuclear structure featuring an eight-coordinate {DyO6N2} core with a distorted triangular dodecahedral geometry. The Sm3+ and Dy3+ complexes exhibit dual-mode luminescence, combining residual ligand-centered blue fluorescence with characteristic Ln3+-centered 4f–4f emission. This spectral balance yields purple-pink emission for the Sm3+ complex and near-ideal white-light emission for the Dy3+ analogue, with 1931 Commission Internationale de l’Éclairage coordinates of (0.343, 0.330), a correlated color temperature of 5012 K, and a high color rendering index of 94. Visible-region ΦLnL values are 7% for the Sm3+ complex and 14% for the Dy3+ analogue, with both complexes showing NIR emission. The dual-emissive behavior may arise from incomplete intramolecular intersystem crossing and Ln3+-dependent ligand-to-metal energy transfer efficiency. This work validates methoxy-functionalized coumarin as an efficient sensitizer unit and demonstrates a ternary heteroleptic approach to achieving single-component white-light and NIR luminophores.