Circularly Polarized Luminescent Eu4(LR)4 Cage for Enantiomeric Excess and Concentration Simultaneous Determination of Chiral Diamines.

Abstract

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 ↔ 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.