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.一种含刺激响应型客体的螺吡喃（spiropyran）-紫精（viologen）单元，可与24元冠醚（24-membered crown ether）组装形成具有部分穿入构型的稳定主客体复合物（host–guest complex）。加入酸可诱导该客体转变为部花菁（merocyanine）物种，激活第二识别位点，适于准轮烷（pseudorotaxane）的形成。两个识别位点的同时存在，会引发大环发生小幅度的穿梭运动，穿梭路径为从紫精单元至部花菁基团。加入碱则可使客体恢复为螺吡喃构型，与此同时该穿梭运动也将停止。