Isomeric [2]rotaxanes and unidirectional [2]pseudorotaxane composed of α-cyclodextrin and aliphatic chain-linked carbazole-viologen compounds

Abstract

(Chemical Equation Presented) Capping the α-cyclodextrin (α-CD) complex of 1-(N-carbazole)-10-[4-(4-pyridinio)-1-pyridinio]decane with 3,5-dimethoxybenzyl bromide in DMF gives two isomeric [2]rotaxanes, 2a and 2b, while α-CD and 1-(N-carbazole)-10-[4-(1-methyl-4-pyridnino)-1-pyridinio] decane 3 in water form mostly a unidirectional [2]pseudorotaxane having the same α-CD orientation as 2b. Structures were elucidated from 1H NMR and circular dichroism spectra. The orientational specificity of α-CD in the 3/α-CD [2]pseudorotaxane is due to the slow dethreading rate of the 2b-type isomer.