Supramolecular Assembly of Chiral Lanthanide Triple-Decker Metallocyclophanes Ln₃(L^meta)₃(L^R/S)₃or Tetrahedral Cages Ln₄(L^para)₄(L^R/S)₄and Their Chiroptical Properties

Two new ligands (L^meta: meta-tris-β-diketonate and L^para: para-tris-β-diketonate) with meta and para orientations of coordinating bidentate β-diketonate units were synthesized in order to investigate their supramolecular formation behavior. When chiral (R)- or (S)-BINAPO (L^R/S) was used as a chiral inducer, trinuclear triple-decker metallocyclophane, Eu₃(L^meta)₃(L^R/S)₃, was formed from L^meta,whereas a tetranuclear tetrahedral cage Eu₄(L^para)₄(L^R/S)₄was formed with L^para. The X-ray crystal of Eu₃(L^meta)₃(L^S)₃shows that all three Eu centers possess the same configuration, hence resulting in homochiral ΔΔΔ assembly. The triple-decker exhibited a longer luminescence lifetime (∼0.98 ms vs ∼0.74 ms) and higher quantum yields (∼66% vs ∼50%) than the tetrahedral cage. Moreover, chiroptical properties were observed for a lanthanide triple-decker metallocyclophane: Mirror-image circular dichroism of chiral Eu₃(L^meta)₃(L^R/S)₃or Eu₄(L^para)₄(L^R/S)₄discloses their enantiomeric behavior and chiral transmission from (R)- or (S)-BINAPO moiety to achiral L^metaand L^para. Furthermore, their circularly polarized luminescence indicated that the |g_lum| can reach 0.13 for the triple-decker metallocyclophane and 0.16 for the tetrahedral cage.