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.

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.