Manipulating stereo-communication in binaphthol-bridged - and -cyclodextrins to develop -selective chiroptical pH switching and anion sensing in water

Molecular structures comprising naturally-occurring, stereodefined cyclodextrins and binaphthyls as bridging units have been realized, designed in such a way that the stereocommunication mode between the two chiral entities is unfavourable ('chiral mismatch'). The induced strain translates into highly responsive chiroptical behavior. On one side, the binaphthol-containing structure functions as a pH-controlled, single-molecule chiroptical switch, with reversal of the optical activity from acidic to basic conditions in a fully reversible manner. Additionally, the same host molecule demonstrates a pronounced chiroptical response to perrhenate in aqueous solution at pH 2.5, showing excellent selectivity for this specific anion. Computational analysis confirmed that the major effect of ReO₄^– complexation is making new conformations accessible to the binaphthol moiety with a large variation of the associated dihedral angles.