RESUMO
Undoubtably, it is challenging to simultaneously determine the identity, enantiomeric excess (ee), and total concentration of an enantiomer by just one optical measurement. Herein, we design a chiral tetrahedron Eu4(LR)4 with circularly polarized luminescence (CPL), which presents highly selective/stereoselective, rapid, and "turn-on" CPL response to chiral diamines, rather than the monoamino compounds, such as monoamines or amino alcohols. By recording the left- and right-CPL intensities of the Eu3+ ion at 591 nm, the enantiomeric composition and concentration of chiral diamines can be simultaneously determined by monitoring the glum value and total emission intensity (IL + IR), respectively. Spectroscopy analyses demonstrate that the variations of glum depend on the inversion and maintenance of configuration around the Eu3+ ion (Δ â Λ), while the "turn-on" response arises from the raising of the T1 state of the ligand. The molecule/electron structural variations are proposed from the synergetic supramolecular interactions of NH2 groups with pendant diols and trifluoroacetyl groups.
RESUMO
Chiral supramolecular lanthanide-helicates are regarded as promising chiroptical materials due to their combination of ground and excited state chirality and special luminescence properties from Ln3+, named circularly polarized luminescence (CPL). However, the sophisticated and costly asymmetric syntheses decelerate their research progress. Herein, a chiral induction strategy is employed to break the racemic equilibrium of lanthanide helicate by the formation of a compact ion pair. The synthesized chiral guanidine cation ((R/S)-HG) helps to effectively transfer chirality to anionic quadruple-stranded helicate by electrostatic, H bonds, and multiple C-Hâ¯F and N-Hâ¯F interactions. The diastereoselective control was confirmed by X-ray crystallography and CD and CPL spectroscopy, where (S)-HG prefers to bind a P (ΔΔ) helical enantiomer, in contrast a M helicate for (R)-HG. Additionally, the inconsistency of CD and CPL spectra in assessing the perturbation of a racemic equilibrium discloses their complementary advantages on monitoring molecular chirality. In the case of diastereomeric enrichment equilibrium, three pairs of helicates show high luminescence quantum yields of 42%-54%, and large |glum| with the values of 0.137-0.266. This work provides an effective strategy to synthesize excellent CPL materials based on racemic lanthanide helicate.
