A bis-spiropyran-containing multi-state [2]rotaxane with fluorescence output

In this paper, a bis-spiropyran-functionalized [2]rotaxane with a 4-morpholin-naphthalimide fluorophore as stopper was designed, synthesized, and studied. The macrocycle can shuttle reversibly in response to external acid–base stimuli and the spiropyran functional group can be switched to its ring-opened merocyanine (MC) state. It has been shown that, by introducing two spiropyran units into the system, intercomponent interactions, such as electron transfer and energy transfer processes, between the SP or MC functional units and the fluorophore, can be altered in response to the combination of acid–base and photochemical stimuli, which can generate obvious UV/vis absorption and fluorescence spectral changes.