Shuttling Motion in a Host-Guest Complex Triggered by Spiropyran to Merocyanine Reversible Chemical Transformation.

A stimulus-responsive guest-containing spiropyran and viologen unit assembles with a 24-membered crown ether into a stable host-guest complex displaying a partially threaded geometry. Acid addition induces guest transformation to a merocyanine species activating a second recognition site, suitable for the formation of a pseudorotaxane. The simultaneous presence of two recognition sites produces a small-amplitude macrocycle shuttling motion, from the viologen to the merocyanine moiety. Base addition returns the guest to its spiropyran form, and concurrently the translation motion stops.

Coupled molecular motions driven by light or chemical inputs: spiropyran to merocyanine isomerisation followed by pseudorotaxane formation.

We have designed and prepared a new dual stimuli-responsive guest molecule containing a spiropyran fragment and a pyridinium moiety. Acid addition or UV-light irradiation induces guest transformation to a merocyanine isomer, promoting the threading motion through a 24-crown-8 macrocycle and the formation of a [2]pseudorotaxane complex.