A light-driven pseudo[4]rotaxane encoded by induced circular dichroism in a hydrogel

A light-driven pseudo[4]rotaxane 1, based on alpha-cyclodextrin (alpha-CyD) and cucurbit[7]uril (CB[7]), is prepared in an easy and convenient manner. The reference pseudo[2]rotaxane 2 and pseudo[3]rotaxane 2' are obtained via the insertion of alpha-CyD and CB[7] onto the dumbbell 3, thus including an azobenzene unit and two viologen moieties, respectively. The CyD macrocycle in pseudo[4]rotaxane 1 can be photochemically stimulated to shuttle accompanied with obvious induced circular dichroism (ICD) signals. The ICD performances of these pseudorotaxanes, including ICD in aqueous solution, variable-temperature ICD, ICD in confected hydrogel systems and in solid-state films, are investigated for their conformational identification. The photo-driven shuttling of the CyD macrocycle in pseudo[4]rotaxane 1 is easier than in the CyD-based psuedo[2]rotaxane 2, especially in non-solution media. This can be attributed to the space exploitation of CB[7]-included parts, which aid the movement of alpha-CYD.