Modulating the Inclusive and Coordinating Ability of Thiacalix[4]arene and Its Antenna Effect on Yb[sup.3+]-Luminescence via Upper-Rim Substitution

The present work introduces the series of thiacalix[4]arenes (H[sub.4]L) bearing different upper-rim substituents (R = H, Br, NO[sub.2]) for rational design of ligands providing an antenna-effect on the NIR Yb[sup.3+]-centered luminescence of their Yb[sup.3+] complexes. The unusual inclusive self-assembly of H[sub.3]L[sup.−] (Br) through Br...π interactions is revealed through single-crystal XRD analysis. Thermodynamically favorable formation of dimeric complexes [2Yb[sup.3+]:2HL[sup.3−]] leads to efficient sensitizing of the Yb[sup.3+] luminescence for H[sub.4]L (Br, NO[sub.2]), while poor sensitizing is observed for ligand H[sub.4]L (H). X-ray analysis of the single crystal separated from the basified DMF solutions of YbCl[sub.3] and H[sub.4]L(NO[sub.2]) has revealed the transformation of the dimeric complexes into [4Yb[sup.3+]:2L[sup.4−]] ones with a cubane-like cluster structure. The luminescence characteristics of the complexes in the solutions reveal the peculiar antenna effect of H[sub.4]L(R = NO[sub.2]), where the triplet level at 567 nm (17,637 cm[sup.−1]) arisen from ILCT provides efficient sensitizing of the Yb[sup.3+] luminescence.