Exceptionally Long‐Lived Luminescence Emitted from TbIII Ion Caged in an AgI–TbIII–Thiacalix[4]arene Supramolecular Complex in Water

The compositions and photophysical properties of luminescent ternary complexes of thiacalix[4]arene‐p‐sulfonate (TCAS), Tb^III, and Ag^I ions were determined. At pH 6, Ag^I₂?Tb^III₂?TCAS₂ formed. Moreover, at pH 10, in the presence of a 20‐fold excess of Ag^I and a 50‐fold excess of TCAS with respect to Tb^III, Ag^I₂?Tb^III?TCAS₂ formed as the main luminescent species. The structure of these complexes was proposed: two TCAS ligands are linked by two S–Ag^I–S linkages to adopt a double‐cone supramolecular structure. Furthermore, each Tb^III ion in the former complex accepts O^?, S, O^? donation, whereas in the latter, the Tb^III center accepts eightfold O^? donation. The luminescence quantum yield (Φ) of Ag^I₂?Tb^III₂?TCAS₂ (0.16) was almost equal to that of Tb^III?TCAS, but the luminescence lifetime τ of the former (=1.09 ms) was larger than that of the latter. For Ag^I₂?Tb^III?TCAS₂, the yield Φ (=0.11) was small, which is attributed to the low efficiency of photosensitization (η=0.11). However, the τ value (4.61 ms) was exceptionally large and almost equal to the natural luminescence lifetime of Tb^III (4.7 ms), which is due to the absence of coordinating water molecules (q=0.1). This is compatible with the proposed structure in which the Tb^III ion is shielded by a supramolecular cage that expels coordinated water molecules responsible for luminescence quenching.