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

Abstract

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(I) (2)Tb(III) (2)TCAS(2) 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(I) (2)Tb(III)TCAS(2) 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 (Phi) of Ag(I) (2)Tb(III) (2)TCAS(2) (0.16) was almost equal to that of Tb(III)TCAS, but the luminescence lifetime tau of the former (=1.09 ms) was larger than that of the latter. For Ag(I) (2)Tb(III)TCAS(2), the yield Phi (=0.11) was small, which is attributed to the low efficiency of photosensitization (eta=0.11). However, the tau 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.