Adaptive helicity and chiral recognition in bright europium quadruple-stranded helicates induced by host-guest interaction
Marzio Rancan, Jacopo Tessarolo, Alice Carlotto, Silvia Carlotto, Maria Rando, Lucrezia Barchi, Elisa Bolognesi, Roberta Seraglia, Gregorio Bottaro, Maurizio Casarin, Guido H. Clever, Lidia Armelao
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 [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.