Adaptive helicity and chiral recognition in bright europium quadruple-stranded helicates induced by host-guest interaction

Chiral information transfer is crucial to design new functions like, for instance, sensing through chiroptical probes in which the input is readout as a consequence of a chiral recognition event. Herein, we report lanthanide quadruple-stranded helicates [Ln2L4]2− that show a guest-to-host chirality transfer. As confirmed by X-ray diffraction (XRD) and density functional theory (DFT) calculations, these cages are present in solution as an equilibrating racemic mixture of left- and right-handed helicates. The helicates adapt their helical conformation by encapsulation of a chiral guest enabling also straightforward enantiomeric excess determination. Asymmetric induction is demonstrated by circular dichroism (CD) and circularly polarized luminescence (CPL), and a helicity inversion mechanism based on a Bailar twist is proposed and studied by DFT calculations. The presented research contributes to the design of helicates with a unique combination of confined cavities, adaptive chirality, and peculiar luminescent properties, finding applications toward the development of optical probes for selective chiral sensing via molecular recognition.