Unidirectional α-cyclodextrin-based [2]rotaxanes bearing viologen unit on axle

1-(2-Carboxyethyl)-1′-(10-carbazole-9-yl-decyl)-4,4′-bipyridinium dibromide 2 forms a unidirectional [2]pseudorotaxane with α-cyclodextrin (α-CD) in water. Condensation of 2/α-CD [2]pseudorotaxane with 4-amino-1-naphthalenesulfonate or 6-amino-β-CD provided the unidirectional [2]rotaxanes 3 and 4, in which the secondary face of α-CD is oriented toward the viologen moiety. The structures were elucidated from two-dimensional ROESY and circular dichroism spectra.