Thiacalix[4]arene-Sandwiched Sandglass-like Ln 9 Clusters (Ln = Tb and Eu): Insights into the Selective Luminescence Quenching Properties by p -Nitrobenzene Derivatives.

Nonanuclear lanthanide clusters Ln 9 (Ln = Tb and Eu) based on p - tert -butylthiacalix[4]arene (H 4 TC4A) have been synthesized by the solvothermal reaction and were structurally determined by single-crystal X-ray diffraction. The framework of Ln 9 can be termed as a sandglass-like structure whose two Ln 4 -TC4A polynuclear secondary building units are bridged by one octa-coordinate {Ln(μ 3 -O) 8 } unit. Efficient TC4A-to-Ln energy transfer was observed for Tb 9 but not for Eu 9 . The luminescence quantum yield (QY) of Tb 9 in the solid state at room temperature was determined to be 17.6%, while its highest QY in a methanolic solution (2 × 10 -5 mol/L) is 59.2% upon excitation at 318 nm. The luminescence of Tb 9 was quenched selectively by derivatives of p -nitrobenzene, as demonstrated by the results of photoluminescence and UV-vis titration experiments and supported by density functional theory calculations. We believe that the interactions between the analyte molecules and the pocket of Tb 9 are primarily responsible for the observed quenching. As such, this work represents one of the few examples of utilizing structurally interesting lanthanide cluster complexes as a sensory platform for the recognition of meaningful analytes and portends the further development of lanthanide-calixarene-complex-based functional materials.