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

Abstract

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 [Ln 2 L 4 ] 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. • Helicates adapt in response to a recognition process in a confined space • Chiral recognition through host-guest events detected by CD and CPL • Very bright europium helicates with luminescence visible to naked eye • Helicity inversion mechanism, i.e., Bailar twist, is revealed by DFT calculations Rancan et al. report chirality transfer for chiroptical molecular recognition. Very bright europium helicates enable a chiroptical readout toward chiral guests. Helicates adapt their conformation with a guest-to-host hierarchical chirality transfer. The molecular recognition process is detected by induced circular dichroism (CD) and circularly polarized luminescence (CPL).