Effect of π-system on long-range photoinduced electron transfer in through-ring α-cyclodextrin complexes of carbazole-viologen linked compounds

Carbazole-viologen linked compounds, with long spacers (ca. 2 nm), were incorporated into two α-cyclodextrins to afford rotaxane type complexes. In the presence of a biphenyl unit in the spacer, the fluorescence lifetime of the carbazole moiety was reduced by 2 ns as compared with the case with a simple alkyl spacer (τ = 12 ns). Contribution of the superexchange mechanism to long-range electron transfer from the carbazole to the viologen moiety was suggested.