Induced Circular Dichroism Spectrum of α-Cyclodextrin Complex with Heptylviologen

The rotational strength of α-cyclodextrin (α-CDx) complex with heptylviologen (1,1′-diheptyl-4,4′-bipyridinium dibromide) was calculated by using the Kirkwood–Tinoco expression. The calculation shows that electric transition polarized along the long axis of heptylviologen gives negative induced circular dichroism (ICD) whereas the short-axis polarized transition gives positive ICD, when HV is axially included in α-CDx and the electric transition moment is located out of the cavity of α-CDx (above the narrower rim). From the comparison between the experimental and calculated results, it is concluded that the heptyl chain of heptylviologen is involved in the cavity while the pyridinium part is situated out of the cavity.