Möbius Zn(II)-Hexaphyrins Bearing a Chiral Coordinating Arm: A Chiroptical Switch Featuring P/M Twist Inversion Controlled by Achiral Effectors.

By their conformational flexibility, Mobius aromatic hexaphyrins provide a dynamic chirality attractive to develop stimuli responsive systems such as chiroptical switches. A regular [28]hexaphyrin has been equipped with a chiral coordinating arm to achieve transfer of chirality from a fix stereogenic element to the dynamic Mobius one. The arm allows straightforward formation of labile monometallic Zn(II) complexes with an exogenous ligand, either a carboxylato or an amino with opposite inwards / outwards orientations relative to the Mobius ring. As a corollary, the chiral coordinating arm is constrained over the ring or laterally, inducing opposite P and M Mobius configurations with unprecedented high stereoselectivity (diast. excess greater than 95 %). By tuning the transfer of chirality, these achiral effectors generate electronic circular dichroism spectra with bisignate Cotton effect of opposite signs. Switching between distinct chiroptical states was ultimately achieved in mild conditions owing to ligand exchange, with high robustness (10 cycles).