Structural and photophysical properties of a two-dimensional europium(III) coordination network with a diyne-based ligand

We report herein the structural and photophysical properties of a novel two-dimensional europium(III) coordination network (EuCN) constructed from a rigid diyne-based dicarboxylate ligand. Single-crystal X-ray diffraction reveals a layered structure in which Eu³⁺ ions adopt an eight-coordinate environment linked via monodentate carboxylates and nitrate anions. The rigid, π-conjugated ligand enables the sensitization of the Eu³⁺ center via the antenna effect, leading to characteristic Eu³⁺ red emission. Judd–Ofelt analysis (Ω₂ > Ω₄) confirms both the significant covalent character of the Eu³⁺–H₂L1 interaction and the asymmetric coordination environment around the Eu³⁺ ion. Photophysical studies show an overall quantum yield of 29 % and a sensitization efficiency of 78 % in DMSO, surpassing solid-state values of 13 % and 55 %, respectively. The improved luminescent performance in dispersion relative to the solid state is attributed to reduced nonradiative deactivation, as supported by lower nonradiative decay rates and longer lifetimes. Crystallographic evidence of coordinated water molecules suggests vibrational quenching contributes to the modest emission efficiency in the solid. Time-dependent density functional theory (TD-DFT) calculations, employed due to the prohibitive size of the system for higher-level methods, provide theoretical support for the antenna mechanism by identifying viable ligand triplet states and ligand-to-metal charge transfer (LMCT) pathways. By integrating experimental and theoretical methods, this study demonstrate how structural features influence photophysical behavior in lanthanide coordination networks.