Flexible Ligand‐Based Lanthanide Three‐Dimensional Metal–Organic Frameworks with Tunable Solid‐State Photoluminescence and OH‐Solvent‐Sensing Properties

Luminescent 3D metal–organic frameworks (MOFs) constructed from trivalent lanthanides Nd3+, Sm3+, Eu3+, Gd3+, Tb3+ and a flexible ligand, 2‐methylsuccinate, (Ln‐msucc) have been hydrothermally obtained as polycrystalline solids. They were fully characterized by X‐ray powder diffraction, thermal analysis, vibrational spectroscopy, and scanning electron microscopy. The crystalline structure and topological features were elucidated and compared with those of related Ln‐MOFs. The magnetic studies reveal that Nd‐msucc and Gd‐msucc present antiferromagnetic and ferromagnetic behavior, respectively. Moreover, the solid‐state photoluminescence properties of all the compounds were fully explored. Depending on the lanthanide content, these materials exhibited luminescence in the near‐infrared and visible regions. In particular, the photophysical behavior of the Eu phase was exhaustively examined and the radiative and nonradiative constants and intrinsic quantum yields were calculated. The hypersensitive nature of the Eu3+ 5D0→7F2 transition allowed an in‐depth study of the optical response in the presence of various protic and aprotic solvents. As far as we know, the chemical‐sensing studies employing Eu‐msucc constitute the first case reported for a lanthanide succinate‐derived framework. The obtained results are promising for the elaboration of specific chemical sensors based on this material. MOFs based on Nd3+/Sm3+/Eu3+/Gd3+/Tb3+ and 2‐methylsuccinate (msucc) were obtained and fully characterized. Magnetic properties and solid‐state photoluminescence were explored. The chemical‐sensor activity of Eu‐msucc was studied in the presence of protic/aprotic solvents regarding quenching effects, intrinsic quantum yields, radiative/nonradiative constants, lifetimes, and intensity transitions.