Supramolecular assembly of chiral lanthanide triple-decker metallocyclophanes Ln₃(Lᵐᵉᵗᵃ)₃(Lᴿ/ˢ)₃ or tetrahedral cages Ln₄(Lᵖᵃʳᵃ)₄(Lᴿ/ˢ)₄ and their chiroptical properties

Abstract

Two new ligands (Lmeta: meta-tris-β-diketonate and Lpara: 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 (LR/S) was used as a chiral inducer, trinuclear triple-decker metallocyclophane, Eu3(Lmeta)3(LR/S)3, was formed from Lmeta, whereas a tetranuclear tetrahedral cage Eu4(Lpara)4(LR/S)4 was formed with Lpara. The X-ray crystal of Eu3(Lmeta)3(LS)3 shows 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(Lmeta)3(LR/S)3 or Eu4(Lpara)4(LR/S)4 discloses their enantiomeric behavior and chiral transmission from (R)- or (S)-BINAPO moiety to achiral Lmeta and Lpara. Furthermore, their circularly polarized luminescence indicated that the |glum| can reach 0.13 for the triple-decker metallocyclophane and 0.16 for the tetrahedral cage.