Luminescent Ln-based silsesquioxanes with a β-diketonate antenna ligand: toward the design of efficient temperature sensors.

We report the synthesis and single-crystal X-ray diffraction, magnetic, and luminescence measurements of a novel family of luminescent cage-like tetranuclear silsesquioxanes (PhSiO)(LnO)(O)(CHO)(EtOH)(CHCN)⋅2CHCN (where Ln = Tb, ; Tb/Eu, ; and Gd, ), featuring seven-coordinated lanthanide ions arranged in a one-capped trigonal prism geometry. Compounds and exhibit characteristic Tb and Tb/Eu-related emissions, respectively, sensitized by the chelating antenna acetylacetonate (acac) ligands upon excitation in the UV and visible spectral regions. Compound is used to assess the energies of the triplet states of the ligand. For compound , theoretical calculations on the intramolecular energy transfer and multiphonon rates indicate a thermal balance between the D Stark components, while the mixed Tb/Eu analog , with a Tb:Eu ratio of 3:1, showcases intra-cluster Tb-to-Eu energy transfer, calculated theoretically as a function of temperature. By utilizing the intensity ratio between the D→F (Tb) and D→F (Eu) transitions in the range 11-373 K, we demonstrate the realization of a ratiometric luminescent thermometer with compound , operating in the range 11-373 K with a maximum relative sensitivity of 2.0% K at 373 K. These findings highlight the potential of cage-like silsesquioxanes as versatile materials for optical sensing-enabled applications.